Official NTA Question PaperFull Solved Paper2020Paper 1
JEE Advanced 2020 Paper 1 Question Paper with Solutions
Official solved question paper for Joint Entrance Examination (Advanced). Review all 54 questions, official answer keys, and detailed step-by-step solutions below, or attempt online with timer and negative marking.
An open-ended U-tube of uniform cross-sectional area contains water (density 103 kg m−3
). Initially the
water level stands at 0.29 m from the bottom in each arm. Kerosene oil (a water-immiscible liquid) of
density 800 kg m−3
is added to the left arm until its length is 0.1 m, as shown in the schematic figure
below. The ratio (h2h1) of the heights of the liquid in the two arms is :
A
1415
B
3335
C
67
D
45
Official Correct Answer:Option (B)
Step-by-Step Solution:
We have, h1 + h2 = 0.29 × 2 + 0.1
h1 + h2 = 0.68 .......(i)
⇒ p0 + ρkg(0.1) +ρwg(h1− 0.1) −ρwgh2 = p0
where, ρk = density of kerosene and ρw = density of water.
A stationary tuning fork is in resonance with an air column in a pipe. If the tuning fork is moved with
a speed of 2 ms−1
in front of the open end of the pipe and parallel to it, the length of the pipe should
be changed for the resonance to occur with the moving tuning fork. If the speed of sound in air is
320 ms−1, the smallest value of the percentage change required in the length of the pipe is
____________.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 0.62to0.63
Official Correct Answer:0.62to0.63
Step-by-Step Solution:
f∝l11⇒f=l1k ....(i)
(where, l1⇒ initial length of pipe)
(v−vTv)f=l1k ....(ii)
(where, vT = speed of tuning fork, l2 = new length of pipe)
Dividing Eq. (i) by Eq. (ii), we get
cv−vT=l1l2⇒l1l2−1=vv−vT−1
l1l2−l1=v−vT
l1l2−l1×100=320−2×100=−0.625
Therefore, smallest value of percentage change required in the length of pipe is 0.625.
Q 3PhysicsSection B • Numericalproperties of matter
+4 / -2
As shown schematically in the figure, two vessels contain water solutions (at temperature T) of
potassium permanganate (KMnO4) of different concentrations n1 and n2 (n1 > n2) molecules per
unit volume with Δn = (n1 − n2) << n1. When they are connected by a tube of small length l and
cross-sectional area S, KMnO4 starts to diffuse from the left to the right vessel through the tube.
Consider the collection of molecules to behave as dilute ideal gases and the difference in their partial
pressure in the two vessels causing the diffusion. The speed v of the molecules is limited by the
viscous force −βv on each molecule, where β is a constant. Neglecting all terms of the order (Δn)2,
which of the following is/are correct? (kB is the Boltzmann constant)
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
n1>>(n1−n2)=Δn
∵p1=NAn1RT and p2=NAn2RT
F=(n1−n2)kBTS=ΔnkBTS
V=βΔnkBTS
ΔnkBTS=ln1Sβv
⇒n1βvl=ΔnkBT
Total number of molecules/second
=dt(n1vdt)S
=n1vS=βvlΔnkBTvS=(lΔn)(βkBT)S
As Δn will decrease with time, therefore rate of molecules getting transfer decreases with time.
Q 4PhysicsSection B • Numericalheat and thermodynamics
+4 / -2
The filament of a light bulb has surface area 64 mm2
. The filament can be considered as a black
body at temperature 2500 K emitting radiation like a point source when viewed from far. At night
the light bulb is observed from a distance of 100 m. Assume the pupil of the eyes of the observer to
be circular with radius 3 mm. Then
Here, A = 64 mm2, T = 2500K (where, A = surface area of filament, T = temperature of filament, d is distance of bulb from observer and Re = radius of pupil of eye)
Point source, d = 100 m, Re = 3 mm
(a) P = σAeT−4
= 5.67 × 10−8× 64 × 10−6× 1 × (2500)4
(∵ e = 1 for black body)
= 141.75 W
(b) Power reaching to the eye
= 4πd2P×(πRe2)
=4π×(100)2141.75×π×(3×10−3)2
=3.189375×10−8 W
(c) λmT=b
λm×2500=2.9×10−3
⇒λm=1.16×10−6 = 1160 nm
(d) Power received by one eye of observer = (λhc)×ΔtΔN
where, ΔtΔN = number of photons.
entering into eye per second.
=3.189375×10−8
=1740×10−96.63×10−34×3×108×ΔtΔN
⇒ΔtΔN=2.79×1011
Q 5PhysicsSection B • Numericalelectrostatics
+4 / -0
One end of a spring of negligible unstretched length and spring constant k is fixed at the origin (0, 0).
A point particle of mass m carrying a positive charge q is attached at its other end. The entire system
is kept on a smooth horizontal surface. When a point dipole p pointing towards the charge q is fixed
at the origin, the spring gets stretched to a length l and attains a new equilibrium position (see figure
below). If the point mass is now displaced slightly by Δl << l from its equilibrium position and
released, it is found to oscillate at frequency δ1mk. The value of δ is ______.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 3.14
Official Correct Answer:3.14
Step-by-Step Solution:
Electrostatic force = Spring force
At l, Fe=Fspkl=l32αpq (Here, α=4πε01)
Now, the mass m is displaced by Δl = x from the mean position.
Fnet=Fsp−Fe=k(l+x)−(l+x)3q(2αp)
=k(x+1)−l3(l+x/l)3q(2αp)
=kx+kl−q(l32αp)(1−l3x)
=kx+kl−q(l32αp)+l32αp.l3x
Substituting l32αpq=kl, we get
Fnet=kx+kl(l3x)=4kx
This is restoring in nature.
Hence, keq=4k
or T=2π4km=πkm
∴f=π1mk
So, δ=π=3.14
Q 6PhysicsSection B • Numericalatoms and nuclei
+4 / -2
A particle of mass m moves in circular orbits with potential energy V(r) = Fr, where F is a positive
constant and r is its distance from the origin. Its energies are calculated using the Bohr model. If the
radius of the particle’s orbit is denoted by R and its speed and energy are denoted by v and E,
respectively, then for the nth orbit (here h is the Planck’s constant)
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
∣Force∣=−drdV⇒F=rmv2 .....(i)
mvr=2πnh .....(ii)
From Eqs. (i) and (ii), we get
∴F=rm(2πmrnh)2∵(v=2πmrnh)
or F=4π2m2r3mn2h2
or F=4π2mr3n2h2
r3∝n2 (as F = constant)
r∝n2/3
v=2πmrnh
v∝n2/3n
or v∝n1/3
∴KE=21mv2=2Fr
∵TE=PE+KE=Fr+2Fr
⇒23Fr=TE
or TE=E=23F×(4π2rnFn2h2)1/3
=23(4π2mn2h2F2)1/3
Q 7PhysicsSection B • Numericalelectrostatics
+4 / -2
A uniform electric field, E=−4003y NC−1
is applied in a region. A charged particle of mass m
carrying positive charge q is projected in this region with an initial speed of 210× 106 ms−1
. This
particle is aimed to hit a target T, which is 5 m away from its entry point into the field as shown
schematically in the figure. Take mq
= 1010 Ckg−1
. Then
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
a=mqE1010×4003m/s2
or a=43×1012m/s2
∴R=au2sin2θ
⇒sin2θ=u2Ra
or sin2θ=4×10×10125×43×1012
⇒sin2θ=23
⇒2θ=60∘,120∘
⇒θ=30∘ or 60∘ for same range
∴T=a2usinθ
=2×43×10122×210×106
⇒T=1210×10−6⇒T=65×10−6
Q 8PhysicsSection B • Numericallaws of motion
+4 / -0
Put a uniform meter scale horizontally on your extended index fingers with the left one at 0.00 cm
and the right one at 90.00 cm. When you attempt to move both the fingers slowly towards the center,
initially only the left finger slips with respect to the scale and the right finger does not. After some
distance, the left finger stops and the right one starts slipping. Then the right finger stops at a distance
xR from the center (50.00 cm) of the scale and the left one starts slipping again. This happens
because of the difference in the frictional forces on the two fingers. If the coefficients of static and
dynamic friction between the fingers and the scale are 0.40 and 0.32, respectively, the value of xR (in
cm) is ______.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 25.60
Official Correct Answer:25.60
Step-by-Step Solution:
Here, μs = 0.40, μk = 0.32
∵μkN3 = μsN4
and x1N3 = 40 × N4
So, x1μk=40μs⇒x10.32=400.4
⇒x10.32=1001⇒x1=32 cm
x1N5μsN5=xgN6μsN6⇒10×320.40×xg0.32
⇒xg=25.6
Q 9PhysicsSection A • MCQrotational motion
+3 / -1
A small roller of diameter 20 cm has an axle of diameter 10 cm (see figure below on the left). It is
on a horizontal floor and a meter scale is positioned horizontally on its axle with one edge of the scale
on top of the axle (see figure on the right). The scale is now pushed slowly on the axle so that it
moves without slipping on the axle, and the roller starts rolling without slipping. After the roller has
moved 50 cm, the position of the scale will look like (figures are schematic and not drawn to scale)
A
B
C
D
Official Correct Answer:Option (C)
Step-by-Step Solution:
For no slipping at ground,
vc = ωR
(where, r is the radius of roller)
∴ Velocity of scale = (vc + ωr) (where, r is the radius of axle)
Given, vc . t = 50 cm
∴ Distance moved by scale = (vc + ωr)t = (vc+rvcr)t=23vc.t=75cm
Therefore, relative displacement (with respect to centre of roller) is (75 − 50) cm = 25 cm.
Q 10PhysicsSection B • Numericalelectrostatics
+4 / -0
A circular disc of radius R carries surface charge density
σ(r)=σ0(1−Rr), where σ0 is a constant
and r is the distance from the center of the disc. Electric flux through a large spherical surface that
encloses the charged disc completely is ϕ0. Electric flux through another spherical surface of radius 4R and concentric with the disc is ϕ. Then the ratio ϕϕ0 is ________.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 6.4
Official Correct Answer:6.4
Step-by-Step Solution:
Let us consider a ring element of radius r and thickness dr.
Surface charge density of disc of radius R,
σ(r)=σ0(1−Rr)
Charge of disc element, dq = σ0(1−Rr)2πrdr
ϕ0=ε0∫dq=ε00∫Rσ0(1−Rr)2πrdr
ϕ0=ε0∫dq=ε00∫R/4σ0(1−Rr)2πrdr
∴ϕϕ0=σ02π0∫R/4(r−Rr2)drσ02π0∫R(r−Rr2)dr
=32R2−3×64R22R2−3R2=532=6.40
Q 11PhysicsSection A • MCQmagnetism
+3 / -1
A light disc made of aluminium (a nonmagnetic material) is kept horizontally and is free to rotate
about its axis as shown in the figure. A strong magnet is held vertically at a point above the disc away
from its axis. On revolving the magnet about the axis of the disc, the disc will (figure is schematic
and not drawn to scale)
A
rotate in the direction opposite to the direction of magnet’s motion
B
rotate in the same direction as the direction of magnet’s motion
C
not rotate and its temperature will remain unchanged
D
not rotate but its temperature will slowly rise
Official Correct Answer:Option (B)
Step-by-Step Solution:
When the magnet is moved, it creates a state, where the plate moves through the magnetic flux, due to which an electromotive force is generated in the plate and eddy currents are induced. These currents are such that it opposes the relative motion ⇒ disc will rotate in the direction of rotation of magnet.
Q 12PhysicsSection B • Numericalunits and measurements
+4 / -2
Sometimes it is convenient to construct a system of units so that all quantities can be expressed in
terms of only one physical quantity. In one such system, dimensions of different quantities are given
in terms of a quantity X as follows: [position] = [Xα]; [speed] = [Xβ
]; [acceleration] = [Xp]; [linear
momentum] = [Xq]; [force] = [Xr]. Then
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
[x]=xα⇒vp=time
[v]=xβ
[a]=xp⇒av=time
[p]=xq
[F]=xr
⇒(speedposition)=(accelerationspeed)=(Fp)
⇒xβxα=xαxβ=xrxq
⇒xα−β=xβ−p=xq−r
∴α−β=β−p=q−r
α+p=2β
q+p=β+r
p+q−r=β
Q 13PhysicsSection A • MCQwave optics
+3 / -1
A parallel beam of light strikes a piece of transparent glass having cross section as shown in the figure
below. Correct shape of the emergent wavefront will be (figures are schematic and not drawn to
scale)
A
B
C
D
Official Correct Answer:Option (A)
Step-by-Step Solution:
Clearly middle part of glass is diverging and upper and lower part are conversing so correct shape of the emergent wavefront is as shown in the figure.
Q 14PhysicsSection B • Numericalcurrent electricity
+4 / -2
Shown in the figure is a semicircular metallic strip that has thickness t and resistivity ρ. Its inner
radius is R1 and outer radius is R2. If a voltage V0 is applied between its two ends, a current I flows
in it. In addition, it is observed that a transverse voltage ΔV develops between its inner and outer
surfaces due to purely kinetic effects of moving electrons (ignore any role of the magnetic field due
to the current). Then (figure is schematic and not drawn to scale)
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
All the elements are in parallel.
∴∫drl=R1∫R2ρπxtdx
rl=πρtln(R1R2)
Resistance = tln(R1R2)πρ
∴I=ResistanceV
=πρVtln(R1R2)
eE=rmv2
I=neAVd
ρπrV0tdr=ne(drt)V
⇒V=ρπnerV0
∴E=ermρ2π2n2e2r2V02t2
⇒E=e3r2ρ2π2n2mV02
dV=−Edr⇒dV=−r3Kdr
V=KR1∫R2r−3dr
ΔV=e3ρ2π2n2mV02(r121−r221)
ΔV∝V02
⇒ΔV ∝ I2
( As I∝V0 )
Q 15PhysicsSection A • MCQlaws of motion
+3 / -1
A football of radius R is kept on a hole of radius r (r < R) made on a plank kept horizontally. One
end of the plank is now lifted so that it gets tilted making an angle θ from the horizontal as shown in
the figure below. The maximum value of θ so that the football does not start rolling down the plank
satisfies (figure is schematic and not drawn to scale)
A
sin θ = Rr
B
tan θ = Rr
C
sin θ = 2Rr
D
cos θ = 2Rr
Official Correct Answer:Option (A)
Step-by-Step Solution:
For θmax, the football is about to roll, then N2 = 0 and all the forces (mg and N1) must pass through contact point.
∴cos(90∘−θmax)=Rr
⇒sinθmax=Rr
Q 16PhysicsSection B • Numericalheat and thermodynamics
+4 / -0
Consider one mole of helium gas enclosed in a container at initial pressure P1 and volume V1. It
expands isothermally to volume 4V1. After this, the gas expands adiabatically and its volume becomes
32V1. The work done by the gas during isothermal and adiabatic expansion processes are Wiso and
Wadia, respectively. If the ratio WadiaWiso = f ln 2, then f is ______.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 1.77
Official Correct Answer:1.77
Step-by-Step Solution:
4p1(4V1)5/3=p2(32V1)5/3
p2=4p1(81)5/3=128p1
Wadi=γ−1p1V1−p2V2
=35−1p1V1−128p1(32V1)
=2/3p1V1(3/4)=89p1V1
Wiso=p1V1ln(V14V1)=2p1V1ln2
∴WadiWiso=916ln2
⇒f=916=1.7778≈1.78
Q 17PhysicsSection A • MCQmagnetism
+3 / -1
A circular coil of radius R and N turns has negligible resistance. As shown in the schematic figure,
its two ends are connected to two wires and it is hanging by those wires with its plane being vertical.
The wires are connected to a capacitor with charge Q through a switch. The coil is in a horizontal
uniform magnetic field Bo parallel to the plane of the coil. When the switch is closed, the capacitor
gets discharged through the coil in a very short time. By the time the capacitor is discharged fully,
magnitude of the angular momentum gained by the coil will be (assume that the discharge time is so
short that the coil has hardly rotated during this time)
A
2πNQB0R2
B
πNQB0R2
C
2πNQB0R2
D
4πNQB0R2
Official Correct Answer:Option (B)
Step-by-Step Solution:
Torque experienced by circular loop = M × B
where, M is magnetic moment and B is magnetic field.
∴τ = iπR2NB0
(at the instant shown θ = π/2)
∴τdt = dL = iπR2NB0dt
= QπR2NB0 (∵ idt = Q)
Q 18PhysicsSection B • Numericalproperties of matter
+4 / -0
When water is filled carefully in a glass, one can fill it to a height h above the rim of the glass due to
the surface tension of water. To calculate h just before water starts flowing, model the shape of the
water above the rim as a disc of thickness h having semicircular edges, as shown schematically in the
figure. When the pressure of water at the bottom of this disc exceeds what can be withstood due to
the surface tension, the water surface breaks near the rim and water starts flowing from there. If the
density of water, its surface tension and the acceleration due to gravity are 103 kg m−3
, 0.07 Nm−1
and 10 ms−2
, respectively, the value of h (in mm) is _________.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 3.74
Official Correct Answer:3.74
Step-by-Step Solution:
Pressure at the bottom of disc = Pressure due to surface tension
ρgh=T(R11+R21)
R1>>>R2
So, R11<<<R21 and R2=h/2
∴ρgh=T(R11+R21)=T(0+h/21)
h2=ρg2T⇒h=ρg2T
⇒=103×102×0.07=104×10014×100
h=14 mm = 3.741
Q 19ChemistrySection A • MCQhydrogen
+3 / -1
Which of the following liberates O2 upon hydrolysis?
A
Pb3O4
B
KO2
C
Na2O2
D
Li2O2
Official Correct Answer:Option (B)
Step-by-Step Solution:
(a) ⟶Pb3O4+H2O\buildrel No reaction Pb3O4 is insoluble in water or do not react with water.
(b) ⟶KOH+H2O2+1/2O2KO2+2H2O\buildrel
Potassium superoxide is a strong oxidant, able to convert oxides into peroxides or molecular oxygen. Hydrolysis gives oxygen gas, hydrogen peroxide and potassium hydroxide.
(c) ⟶2NaOH+H2O2Na2O2+2H2O\buildrel
When sodium peroxide dissolves in water, it is hydrolysed and forms sodium hydroxide and hydrogen peroxide. The reaction is highly exothermic.
(d) ⟶2LiOH+H2O2Li2O2+2H2O\buildrel
The reactivity of Li2O2 toward water differs from LiO2, in Li2O2 results in H2O2 as a product.
Hence, the correct option is (b).
Q 20ChemistrySection B • Numericalsolid state
+4 / -2
The cubic unit cell structure of a compound containing cation M and anion X is shown below. When compared to the anion, the cation has smaller ionic radius. Choose the correct statement(s).
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
(a) The empirical formula of the compound :
Contribution of M and X :
M(2×21)X(4×41)⇒MX
(b) Coordination number of both M and X is 8.
(c) Distance between M and X
=4a2+2a2=43a=23a
⇒ 0.866 a
(d) rM:rX=(3−1):1⇒0.732:1, thus statement (d) is incorrect.
Q 21ChemistrySection A • MCQbasics of organic chemistry
+3 / -1
Newman projections P, Q, R and S are shown below :
Which one of the following options represents identical molecules?
A
P and Q
B
Q and S
C
Q and R
D
R and S
Official Correct Answer:Option (C)
Step-by-Step Solution:
IUPAC name of P, Q, R and S are :
IUPAC name of compounds Q and R are same, thus the correct option is (c).
Q 22ChemistrySection B • Numericalaldehydes ketones and carboxylic acids
+4 / -2
In the reaction scheme shown below Q, R and S are the major products.
The correct structure of
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
Compound (P) undergoes Friedel-Craft acylation reaction in presence of succinic anhydride and AlCl3 to gives an acid (Q).
Compound (Q) on treatment with Zn-Hg/HCl undergoes Clemmensen reduction, where ketone group change into alkane and on further reaction with dehydrating agent H3PO4 gives compound (R).
Compound (R) on reaction with Grignard reagent and heated in presence of acid gives dehydrating product (S).
Thus, the option (b) and (d) are correct.
Q 23ChemistrySection A • MCQp block elements
+3 / -1
A colourless aqueous solution contains nitrates of two metals, X and Y. When it was added to an aqueous solution of NaCl, a white precipitate was formed. This precipitate was found to be partly soluble in hot water to give a residue P and a solution Q. The residue P was soluble in aqueous NH3 and also in excess sodium thiosulphate. The hot solution Q gave a yellow precipitate with KI. The metals X and Y, respectively, are
A
Ag and Pb
B
Ag and Cd
C
Cd and Pb
D
Cd and Zn
Official Correct Answer:Option (A)
Step-by-Step Solution:
X : Ag Y : Pb P : AgCl Q : PbCl2
Hence, the correct option is (a).
Q 24ChemistrySection B • Numericalelectrochemistry
+4 / -0
Consider a 70% efficient hydrogen-oxygen fuel cell working under standard conditions at 1 bar and 298 K. Its cell reaction is
⟶H2O(l)H2(g)+21O2(g)\buildrel
The work derived from the cell on the consumption of 1.0 × 10−3 mole of H2(g) is used to compress 1.00 mole of a monoatomic ideal gas in a thermally insulated container. What is the change in the temperature (in K) of the ideal gas?
The standard reduction potentials for the two half-cells are given below :
⟶2H2O(l),O2(g)+4H+(aq)+4e−\buildrel
Eo=1.23V
⟶H2(g),2H+(aq)+2e−\buildrel
Eo=0.00V
Use, F=96500Cmol−1, R=8.314Jmol−1K−1.
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 13.32
Official Correct Answer:13.32
Step-by-Step Solution:
Vessel is insulated, thus q = 0
For the given reaction : \eqalign{
& {H_2}(g) + 1/2{O_2}(g)\buildrel {} \over
\longrightarrow {H_2}O(l); \cr
& {E^o} = 1.23 - 0.00 = 1.23V \cr}
ΔGo = −nFEo
= −2 × 96500 × 1.23 J/mol
Therefore, work derived from this fuel cell using 70% efficiency and on consumption of 1.0 × 10−3 mol of H2(g)
= 2 × 96500 × 1.23 × 0.7 × 1 × 10−3
= 166.17 J
This work done = change in internal energy (for monoatomic gas,
CV′m=3R/2),
166.17=nCV,mΔT
⇒ΔT=1×3×8.314166.17×2
⇒13.32K
Q 25ChemistrySection B • Numericalthermodynamics
+4 / -2
In thermodynamics, the p-V work done is given by
w=−∫dVpext
For a system undergoing a particular process, the work done is
w=−∫dV(V−bRT−V2a)
This equation is applicable to a
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
Given, w=−∫pextdV
For 1 mole van der Walls' gas
p=(V−bRT−V2a)
For reversible process, pext = pgas
w=−∫(V−bRT−V2a)dV
But, it is not applicable for irreversible process which are carried out very fast. So, work done is calculated assuming final pressure remains constant throughout the process. Thus, statement (a), (b) and (c) correct while statement (d) is incorrect.
Q 26ChemistrySection B • Numericalbasics of organic chemistry
+4 / -2
With respect to the compounds I-V, choose the correct statement(s).
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
Triphenylmethane (I) is acidic because its conjugate base is stabilised by resonance.
Cyclopentadiene (IV) is acidic because its conjugate base is aromatic.
Nitrobenzene is more acidic than benzene because nitro group is electron withdrawing. It will stabilise the conjugate base of benzene by −R and −I effect.
The acidic strength order on the basis of pKa data is
IV > V > I > II > III.
Hence, the correct options are (a), (b) and (c) only.
Q 27ChemistrySection B • Numericalcoordination compounds
+4 / -2
Choose the correct statement(s) among the following :
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
(a) In [FeCl4]-, oxidation number of Fe atom = +3
Electronic configuration of Fe in ground state = 3d64s2
Electronic configuration of
Fe3+ = 3d54s04p0
Thus, [FeCl4]- has tetrahedral geometry.
(b) [Co(en)(NH3)2Cl2]+ have three geometrical isomers. Thus, statement (b) is incorrect.
(c) Fe3+ in [FeCl4]- is sp3-hybridised with 5 unpaired electrons. (higher spin-only magnetic moment
= n(n+2) = 5.92 BM). While Co3+ in [Co(en)(NH3)2Cl2]+ is d2sp3-hybridised with zero unpaired electrons (low spin-only magnetic moment = n(n+2) = 0 BM).
Thus, the statement (c) is correct.
(d) Co3+[Co(en)(NH3)2Cl2]+
Co3+ in [Co(en)(NH3)2Cl2]+ is d2sp3-hybridised and has octahedral geometry with 0 unpaired electron. Thus, statement (d) is incorrect.
Q 28ChemistrySection A • MCQgaseous state
+3 / -1
If the distribution of molecular speeds of a gas is as per the figure shown below, then the ratio of the most probable, the average, and the root mean square speeds, respectively, is
A
1 : 1 : 1
B
1 : 1 : 1.224
C
1 : 1.128 : 1.224
D
1 : 1.128 : 1
Official Correct Answer:Option (B)
Step-by-Step Solution:
Fraction of molecules vs velocity graph is Maxwell distribution curve.
This curve is slightly unsymmetrical as shown below.
The ratio of most probable, the average and the root mean square speeds for this graph is 1 : 1.128 : 1.224
But the graph in question is completely symmetrical. Therefore, the most probable and the average speed will be same here but root mean square speed will be greater than average speed. So, the correct ratio is 1 : 1 : 1.224.
Q 29ChemistrySection B • Numericalgaseous state
+4 / -0
Aluminium reacts with sulphuric acid to form aluminium sulphate and hydrogen. What is the volume of hydrogen gas in litre (L) produced at 300 K and 1.0 atm pressure, when 5.4 g of aluminium and 50.0 mL of 5.0 M sulphuric acid are combined for the reaction?
(Use molar mass of aluminium as 27.0 g mol−1, R = 0.082 atm L mol−1 K−1)
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 6.15
Official Correct Answer:6.15
Step-by-Step Solution:
Aluminium reacts with sulphuric acid to form aluminium sulphate and hydrogen.
H2SO4 is limiting reagent and moles of H2(g) produced = 0.25 mol
Using ideal gas equation,
pV = nRT
⇒V=1atm0.25×0.082×300=6.15L
Q 30ChemistrySection A • MCQbasics of organic chemistry
+3 / -1
The Fischer projection of D-erythrose is shown below :
D-erythrose and its isomers are listed as P, Q, R, and S in Column - I. Choose the correct relationship of P, Q, R, and S with D-erythrose from Column - II.
A
P
Q
R
S
2
3
2
2
B
P
Q
R
S
3
1
1
2
C
P
Q
R
S
2
1
1
3
D
P
Q
R
S
2
3
3
1
Official Correct Answer:Option (C)
Step-by-Step Solution:
First of all, we need to convert wedge-dash formula into Fischer projection formula.
Now we can clearly see, that compound P is same as given compound, thus compound P is identical to D-erythrose.
Compound Q and D-erythrose are not mirror images of one another and are non-superimposable on one another. Thus, they are diastereomers.
Compound R and D-erythrose are also not mirror images of one another and are non-superimposable on one another. Thus, they are diastereomers.
Compound S and D-erythrose are chiral molecules. They are mirror images of one another. Furthermore, the molecules are non-superimposable on one another. This means that the molecules cannot be placed on top of one another and give the same molecule. Chiral molecules with one or more stereocenters can be enantiomers.
Hence, the correct option is (c).
Q 31ChemistrySection B • Numericalchemical kinetics and nuclear chemistry
+4 / -0
92238U is known to undergo radioactive decay to form 82206Pb by emitting alpha and beta particles. A rock initially contained 68 × 10−6 g of 92238U. If the number of alpha particles that it would emit during its radioactive decay of 92238U to 82206Pb in three half-lives is Z × 1018, then what is the value of Z?
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 1.2
Official Correct Answer:1.2
Step-by-Step Solution:
⟶82206Pb+824He+6−10β92238U\buildrel
Number of moles of 92238U present initially
= 23868×10−6
After three half-lifes, moles of 92238U decayed
=23868×10−6×(1−231)
=23868×10−6×87
Therefore, number of α-particles emitted
=23868×10−6×87×8×6.023×1023
=1.204×1018
≈1.2×1018
Thus, the correct answer is 1.2.
Q 32ChemistrySection B • Numericalchemical equilibrium
+4 / -0
Consider the reaction,
A ⇌ B
at 1000 K. At time t', the temperature of the system was increased to 2000 K and the system was allowed to reach equilibrium. Throughout this experiment the partial pressure of A was maintained at 1 bar. Given, below is the plot of the partial pressure of B with time. What is the ratio of the standard Gibbs energy of the reaction at 1000 K to that at 2000 K?
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 0.25
Official Correct Answer:0.25
Step-by-Step Solution:
Given : Image
Using ΔG=ΔGo+RTlnKp
At equilibrium : ΔGo=−RTlnKp
ΔG10=−RT1lnKp1 ... (i)
ΔG20=−RT2lnKp2 ...(ii)
From Eqs. (i) and (ii),
ΔG2oΔG1o=T2T1×lnKp2lnKp1
=20001000×ln(100)ln(10)=41=0.25
Q 33ChemistrySection A • MCQbasics of organic chemistry
+3 / -1
Which of the following structures has the IUPAC name
According to the IUPAC rules, first of all select the longest carbon chain (6-carbon atoms) then numbering should be start from most prior functional group, which is carboxylic acid in the given compound, thus
3-ethynyl-2hydroxy-4-methylhex-3-en-5-ynoic acid
Q 34ChemistrySection B • Numericalp block elements
+4 / -2
With respect to hypochlorite, chlorate and perchlorate ions, choose the correct statement(s).
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
(a) Order of acid strength different oxyacids of chlorine are :
Weak acid have strong conjugate base thus hypochlorite ion has strongest conjugate base. Therefore, statement (a) is correct.
(b) Hypochlorite ion is linear and perchlorate ion is tetrahedral and there is no effect of lone pair on hypochlorite ion. Thus, statement (b) is correct.
(c) In the disproportionation reaction, chlorate ion Cl(+5) is oxidised to perchlorate, Cl(+7) and reduce to chloride, Cl(−1).
4ClO3−⟶3ClO4−+Cl−
While in hypochlorite ion, chlorite ion Cl(+1) is oxidised to chlorate, Cl(+5) and reduced to chloride, Cl(−1) ion.
3ClO−⟶ClO3−+2Cl−
Thus, statement (c) is incorrect.
(d) The hypochlorite ion oxidises the sulphite ion to sulphate ion, because HOCl is the strongest oxidising Cloxyacids,
⟶SO42−+Cl−ClO−+SO32−\buildrel
Thus, statement (d) is correct.
Q 35ChemistrySection B • Numericalsome basic concepts of chemistry
+4 / -0
5.00 mL of 0.10 M oxalic acid solution taken in a conical flask is titrated against NaOH from a burette using phenolphthalein indicator. The volume of NaOH required for the appearance of permanent faint pink color is tabulated below for five experiments. What is the concentration, in molarity, of the NaOH solution?
Exp. No.
Vol. of NaOH (mL)
1
12.5
2
10.5
3
9.0
4
9.0
5
9.0
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 0.11
Official Correct Answer:0.11
Step-by-Step Solution:
Oxalic acid solution titrated with NaOH solution using phenolphthalein as an indicator.
⟶Na2C2O4+2H2OH2C2O4+2NaOH\buildrel
Equivalent of H2C2O4 reacted = Equivalent of NaOH reacted
=10005×2×0.1=10009×M(NaOH)×1
M(NaOH)=91=0.11
Q 36ChemistrySection B • Numericalaldehydes ketones and carboxylic acids
+4 / -0
In the following reaction, compound Q is obtained from compound P via an ionic intermediate
What is the degree of unsaturation of Q?
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 18
Official Correct Answer:18
Step-by-Step Solution:
Compound (P) on treatment with concentrated H2SO4, gives intermediate compound, on delocalisation, gives a coloured compound Q.
Number of rings = 4 + 1 = 5
π-bonds = 4 × 3 + 1 = 13
Thus, the degree of unsaturation of Q is 18.
Q 37MathematicsSection B • Numericalmatrices and determinants
+4 / -2
Let M be a 3 × 3 invertible matrix with real entries and let I denote the 3 × 3 identity matrix. If M−1 = adj(adj M), then which of the following statements is/are ALWAYS TRUE?
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
It is given that matrix M be a 3 × 3 invertible matrix, such that
M−1 = adj(adj M) ⇒ M−1 = |M| M
(∵ for a matrix A of order 'n' adj(adjA) = |A|n−2 A}
⇒ M−1 M = |M|M2⇒ M2|M| = I .....(i)
∵ det(M2 |M|) = det(I) = 1
⇒ |M|3|M|2 = 1 ⇒ |M| = 1 .....(ii)
from Eqs. (i) and (ii), we get
M2 = I
As, adj M = |M|M−1 = M
⇒ (adj M)2 = M2 (adj M)2 = I
Q 38MathematicsSection B • Numerical3d geometry
+4 / -2
Let L1 and L2 be the following straight lines.
L1:1x−1=−1y=3z−1 and L2:−3x−1=−1y=1z−1.
Suppose the straight line
L:lx−α=my−1=−2z−γ
lies in the plane containing L1 and L2 and passes through the point of intersection of L1 and L2. If the line L bisects the acute angle between the lines L1 and L2, then which of the following statements is/are TRUE?
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
Equation of given straight lines
L1:1x−1=−1y=3z−1
and L2:−3x−1=−1y=1z−1
having vector form respectively, are
and \eqalign{
& r = (\widehat i + \widehat k) + \lambda (\widehat i - \widehat j + 3\widehat k) \cr
& r = (\widehat i + \widehat k) + v( - 3\widehat i - \widehat j + \widehat k) \cr}
∵(i−j+3k).(−3i−j+k)
= −3 + 1 + 3 = 1 is positive,
∴ Angle between supporting line vectors of lines L1 and L2 is acute, and point of intersection of given lines L1 and L2 is (1, 0, 1)
Now, vector along the acute angle bisector of vectors (i−j+3k) and (−3i−j+k) is (i−j+2k) or (i+j−2k)
It is given that line
L:lx−α=my−1=−2z−γ is the bisector of the acute angle between the lines L1 and L2, so
l = 1 and m = 1
and 1I−α=10−1=−21−γ
⇒α=2,γ=−1
∴α−γ=3,l+m=2
Q 39MathematicsSection B • Numericalproperties of triangles
+4 / -0
In a triangle PQR, let a = QR, b = RP, and c = PQ. If |a| = 3, |b| = 4
and c.(a−b)a.(c−b)=∣a∣+∣b∣∣a∣, then the value of |a × b|2 is ......
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 108
Official Correct Answer:108
Step-by-Step Solution:
It is given that, in a ΔPQR
PQ = c, QR = a and RP = b, so a + b + c = 0
∴ |a|2 + a . b + a . c = 0 ....(i)
and a . b + |b|2 + c . b = 0 ....(ii)
and, also given that |a| = 3, |b| = 4
and c.a−c.ba.c−a.b=∣a∣+∣b∣∣a∣=73
⇒7[(a.c)−(a.b)]=3[(c.a)−(c.b)]
from Eqs. (i) and (ii), on putting the values of a . c and c . b, we get,
⇒7[−9−(a.b)−(a.b)]=3[−9−(a.b)+16+(a.b)]
⇒7[−9−2(a.b)]=3×7
⇒a.b=−6
∵∣a×b∣2=(∣a∣∣b∣)2−(a.b)2
= 144−36=108
Q 40MathematicsSection B • Numericalfunctions
+4 / -0
For a polynomial g(x) with real coefficients, let mg denote the number of distinct real roots of g(x). Suppose S is the set of polynomials with real coefficients defined by
For a polynomial f, let f' and f'' denote its first and second order derivatives, respectively. Then the minimum possible value of (mf' + mf''), where f ∈ S, is ..............
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 5
it have −1 and 1 as repeated roots twice, so graph of f(x) touches the X-axis at x = −1 and x = 1, so f'(x) having at least three roots x = −1, 1 and α. Where α∈(−1, 1) and f''(x) having at least two roots in interval (−1, 1)
So, mf' = 3 and mf'' = 2
∴ Minimum possible value of (mf' + mf'') = 5
Q 41MathematicsSection A • MCQfunctions
+3 / -1
If the function f : R → R is defined by f(x) = |x| (x − sin x), then which of the following statements is TRUE?
A
f is one-one, but NOT onto
B
f is onto, but NOT one-one
C
f is BOTH one-one and onto
D
f is NEITHER one-one NOR onto
Official Correct Answer:Option (C)
Step-by-Step Solution:
The given function f : R → R is
f(x)=∣x∣(x−sinx) .....(i)
∵ The function 'f' is a odd and continuous function and as x→∞limf(x)=∞ and x→∞limf(x)=−∞, so range is R, therefore, 'f' is a onto function.
Similarly, for x < 0, −x + sin x > 0 and (− x) (1 − cos x) > 0, therefore, f′(x)>0∀x∈(−∞,0)
⇒ f is strictly increasing function, ∀x∈(0, ∞)
Therefore 'f' is a strictly increasing function for x∈R and it implies that f is one-one function.
Q 42MathematicsSection B • Numericalsequences and series
+4 / -0
Let m be the minimum possible value of log3(3y1+3y2+3y3), where y1,y2,y3 are real numbers for which y1+y2+y3 = 9. Let M be the maximum possible value of (log3x1+log3x2+log3x3), where x1,x2,x3 are positive real numbers for which x1+x2+x3 = 9. Then the value of log2(m3)+log3(M2) is ...........
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 8
Official Correct Answer:8
Step-by-Step Solution:
For real numbers y1, y2, y3, the quantities 3y1, 3y2 and 3y3 are positive real numbers, so according to the AM-GM inequality, we have
33y1+3y2+3y3≥(3y1.3y2.3y3)31
⇒3y1+3y2+3y3≥3(3y1.3y2.3y3)31
On applying logarithm with base '3', we get
log3(3y1+3y2+3y3)≥[1+31(y1+y2+y3)]
= 1 + 3
= 4
{∵y1+y2+y3 = 9}
∴ m = 4
Now, for positive real numbers x1, x2 and x3 according to AM-GM inequality, we have
Q 43MathematicsSection B • Numericalsequences and series
+4 / -0
Let a1, a2, a3, .... be a sequence of positive integers in arithmetic progression with common difference 2. Also, let b1, b2, b3, .... be a sequence of positive integers in geometric progression with common ratio 2. If a1 = b1 = c, then the number of all possible values of c, for which the equality 2(a1 + a2 + ... + an) = b1 + b2 + ... + bn holds for some positive integer n, is ...........
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 1
Official Correct Answer:1
Step-by-Step Solution:
Given arithmetic progression of positive integers terms a1, a2, a3, ..... having common difference '2' and geometric progression of positive integers terms b1, b2, b3, .... having common ratio '2' with a1 = b1 = c, such that 2(a1 + a2 + a3 + ... + an) = b1 + b2 + b3 + ... + bn
⇒2×2n[2C+(n−1)2]=C(2−12n−1)
⇒2nC+2n2−2n=2n.C−C
⇒C[2n−2n−1]=2n2−2n
∵C∈N⇒2n2−2n≥2n−2n−1
⇒2n2+1≥2n⇒n≤6
and, also C > 0 ⇒ n > 2
∴ The possible values of n are 3, 4, 5, 6
So, at n=3,C=8−6−1(2×9)−6=12
at, n=4,C=16−8−132−8=924=38∈/N
at, n=5,C=32−10−150−10=2140∈/N
and at, n=6,C=64−12−172−12=5160∈/N
∴ The required value of C = 12 for n = 3
so number of possible value of C is 1
Q 44MathematicsSection A • MCQprobability
+3 / -1
Let C1 and C2 be two biased coins such that the probabilities of getting head in a single toss are 32 and 31, respectively. Suppose α is the number of heads that appear when C1 is tossed twice, independently, and suppose β is the number of heads that appear when C2 is tossed twice, independently. Then the probability that the roots of the quadratic polynomial x2− ax + β are real and equal, is
A
8140
B
8120
C
21
D
41
Official Correct Answer:Option (B)
Step-by-Step Solution:
It is given that α is the number of heads that appear when C1 is tossed twice, the probability distribution of random variable α is
Similarly, it is given that β is the number of heads that appear when C2 is tossed twice, so probability distribution of random variable β is
Now, as the roots of quadratic polynomial x2−αx + β are real and equal, so D = α2− 4β = 0 and it is possible if (α, β) = (0, 0) or (2, 1)
∴ Required probability
= (31)2(32)2+(32)2(94)
= 814 + 8116 = 8120
Q 45MathematicsSection B • Numericalfunctions
+4 / -0
Let f : [0, 2] → R be the function defined by
f(x)=(3−sin(2πx))sin(πx−4π)−sin(3πx+4π)
If α,β∈[0,2] are such that {x∈[0,2]:f(x)≥0}=[α,β], then the value of β−α is ..........
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 1
Q 46MathematicsSection A • MCQquadratic equation and inequalities
+3 / -1
Suppose a, b denote the distinct real roots of the quadratic polynomial x2 + 20x − 2020 and suppose c, d denote the distinct complex roots of the quadratic polynomial x2− 20x + 2020. Then the value of
ac(a − c) + ad(a − d) + bc(b − c) + bd(b − d) is
A
0
B
8000
C
8080
D
16000
Official Correct Answer:Option (D)
Step-by-Step Solution:
Given quadratic polynomials, x2 + 20x − 2020 and x2− 20x + 2020 having a, b distinct real and c, d distinct complex roots respectively.
So, a + b = −20, ab = −2020
and c + d = 20, cd = 2020
Now, ac(a −c) + ad(a − d) + bc(b −c) + bd(b − d)
= a2(c + d) − a(c2 + d2) + b2(c + d) − b(c2 + d2)
= (c + d) (a2 + b2) − (c2 + d2) (a + b)
= (c + d)[(a + b)2− 2ab] − (a + b)[(c + d)2− 2cd]
= 20[(20)2 + 4040] + 20[(20)2− 4040]
= 2 × 20 × (20)2 = 40 × 400 = 16000
Q 47MathematicsSection A • MCQparabola
+3 / -1
Let a, b and λ be positive real numbers. Suppose P is an end point of the latus return of the parabola y2 = 4λx, and suppose the ellipse a2x2+b2y2=1 passes through the point P. If the tangents to the parabola and the ellipse at the point P are perpendicular to each other, then the eccentricity of the ellipse is
A
21
B
21
C
31
D
52
Official Correct Answer:Option (A)
Step-by-Step Solution:
Equation of given parabola is
y2 = 4λx ....(i)
So the end point of the latus rectum of the parabola (i), P(λ, 2λ) and the given ellipse a2x2+b2y2=1, passes through point P(λ, 2λ).
On differentiating the equation of parabola, w.r.t. 'x', we get
dxdy=y2λ
∴ Slope of tangent to the parabola at point P is m1 = 1
Similarly, on differentiating the equation of given ellipse, a2x2+b2y2=1, w.r.t.x, we get a22x+b22ydxdy=0⇒dxdy=−a2yb2x
∴ Slope of tangent to the ellipse at point P is m2=−2a2b2
∵ It is given that the tangents are perpendicular to each other. So, m1m2=−1
⇒(1)(−2a2b2)=−1
⇒a2b2=2⇒b=2a
∴ Eccentricity of ellipse a2x2+b2y2=1 will be
e=1−b2a2=1−21=21 {∵ b > a}
Q 48MathematicsSection B • Numericalproperties of triangles
+4 / -2
Let x, y and z be positive real numbers. Suppose x, y and z are the lengths of the sides of a triangle opposite to its angles X, Y, and Z, respectively. If
tan2X+tan2Z=x+y+z2y, then which of the following statements is/are TRUE?
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
For a ΔXYZ, it is given that
tan2X+tan2Z=x+y+z2y
⇒s(s−x)Δ+s(s−z)Δ=sy
⇒Δ(s−x)(s−z)(s−z+s−x)=y
⇒Δ=(s−x)(s−z)
⇒s(s−x)(s−y)(s−z)=(s−x)2(s−z)2
⇒s2−sy=s2−(x+z)s+xz
⇒s(x+z−y)=xz
⇒(x+z)2−y2=2xz
⇒x2+z2=y2⇒y=2π
∵X+Y+Z=π⇒X+Z=2π=Y
⇒X+Z=Y
∵tan2X=1+cosx1−cosx=1+yz1−yz
=y+zy−z=y+zy2−z2
tan2X=y+zx {∵ x2 + z2 = y2}
Q 49MathematicsSection B • Numericalcomplex numbers
+4 / -2
Let S be the set of all complex numbers z satisfying |z2 + z + 1| = 1. Then which of the following statements is/are TRUE?
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
It is given that the complex number satisfying
∣z2+z+1∣=1⇒(z+21)2+43=1
∵∣z1−z2∣≥∣∣z1∣−∣z2∣∣
∴(z+21)2−(−43)≥z+212−−43
⇒z+212−43≤1
⇒−1≤z+212−43≤1
⇒−41≤z+212≤47
⇒0≤z+212≤47 {∵ |z| ≥ 0}
⇒0≤z+212≤27 ....(i)
∵⇒z+21≤27
∵∣z1+z2∣≥∣∣z1∣−∣z2∣∣
∴z+21≥∣z∣−21
⇒∣z∣−21≤z+21≤27
⇒−27≤∣z∣−21≤27
⇒21−7≤∣z∣≤27+1
⇒∣z∣≤21+7, ∴ |z| ≤ 2
∵(z+21)2+43≤z+212+43
⇒1≤z+212+43⇒z+212+43≥1
⇒z+212≥41⇒z+21≥21 ....(ii)
from Eqs. (i) and (ii), we get
21≤z+21≤27
Q 50MathematicsSection B • Numericallimits continuity and differentiability
+4 / -0
let e denote the base of the natural logarithm. The value of the real number a for which the right hand limit
x→0+limxa(1−x)1/x−e−1
is equal to a non-zero real number, is .............
Answer Format:Enter numerical value rounded to the nearest integerOfficial Answer: 1
Q 53MathematicsSection B • Numericallimits continuity and differentiability
+4 / -2
Let the function f : R → R be defined by f(x) = x3− x2 + (x − 1)sin x and let g : R → R be an arbitrary function. Let fg : R → R be the product function defined by (fg)(x) = f(x)g(x). Then which of the following statements is/are TRUE?
Official Correct Answer:Declared in Solution
Step-by-Step Solution:
Given functions f : R → R be defined
by f(x) = x3− x2 + (x + 1) sin x and g : R → R be an arbitrary function.
Now, let g is continuous at x = 1, then
x→1−limx−1(fg)(x)−(fg)(1)
=h→0lim1−h−1(fg)(1−h)−(fg)(1)
∵(fg)(x)=f(x).g(x) (given)
=h→0lim−hf(1−h).g(1−h)−f(1).g(1)
=h→0lim−hf(1−h).g(1)
{∵ f(1) = 0 and g is continuous at x = 1, so g(1 − h) = g(1)}
=g(1)h→0lim−h(1−h)2(−h)+(−h)sin(1−h)
=(1+sin1)g(1)
Similarly, x→1+limx−1(fg)(x)−(fg)(1)
=h→0limhf(1−h).g(1)
=g(1)h→0limh(1+h)2(h)+hsin(1+h)
=(1+sin1)g(1)
∵ RHD and LHD of function fg at x = 1 is finitely exists and equal, so fg is differentiable at x = 1