solution-for-wb-jee-2012 Phy - Chem(Page 21 - 35)

8/11/2019 solution-for-wb-jee-2012 Phy - Chem(Page 21 - 35)

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Q. 1 Q. 30 carry one mark each

1. In a mercury thermometer the ice point (lower fixed point) is marked as 10oand the steam point (upper fixed point) is

marked as 130o. At 40oC temperature, what will this thermometer read?

(A) 78o (B) 66o (C) 62o (D) 58o

Ans : (D)

Hints : 40 0 T 10100 0 130 10

T = 58o

2. The magnetic flux linked with a coil satisfies the relation = 4t2+ 6t + 9 Wb, where t is the time in second. The e.m.f.

induced in the coil at t = 2 second is

(A) 22 V (B) 18 V (C) 16 V (D) 40 V

Ans : (A)

Hints :d

| | 8t 6dt

at t = 2 s. | | = 22 V

3. Water is flowing through a very narrow tube. The velocity of water below which the flow remains a streamline flow is

known as

(A) Relative velocity (B) Terminal velocity (C) Critical velocity (D) Particle velocity

Ans : (C)

4. If the velocity of light in vacuum is 3 108ms1, the time taken (in nanosecond) to travel through a glass of thickness

10 cm and refractive index 1.5 is

(A) 0.5 (B) 1.0 (C) 2.0 (D) 3.0

Ans : (A)

Hints :

88oC 3 10C 2 10 m / s

1.5

2

8

d 10 10t

c 2 10= 0.5 ns

5. A charge +q is placed at the orgin O of X Y axes as shown in the figure. The work done in taking a charge Q from

A to B along the straight line AB is

(A)0

qQ a b

4 ab (B) 0

qQ b a

4 ab (C) 20

qQ b 1

4 ba(D) 2

0

qQ a 1

4 bb

Ans : (A)

Hints : B A0

Qq 1 1W Q V V

4 b a = 0

qQ a b

4 ab

Code -

WBJEE - 2012 (Answers & Hints) Physics & Chemistry

Regd. Office:Aakash Tower, Plot No.-4, Sector-11, Dwarka, New Delhi-110075 Ph.: 011-47623456 Fax : 011-47623472

(1)

ANSWERS & HINTSfor

WBJEE - 2012

SUB : PHYSICS & CHEMISTRY


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(2)

6. What current will flow through 2 k resistor in the circuit shown in the figure?

(A) 3 mA (B) 6 mA (C) 12 mA (D) 36 mA

Ans : (A)

Hints : Req

6 36 8k

6 3,

3

3

V 72I 9 10 A

R 8 10,

31

1I I 3 10 A

3, I

1= current through 2 k

7. In a region, the intensity of an electric field is given by E 2i 3j k in NC1. The electric flux through a surface

S 10i m2in the region is

(A) 5 Nm2C1 (B) 10 Nm2C1 (C) 15 Nm2C1 (D) 20 Nm2C1

Ans : (D)

Hints : e E.S = 20 Nm2C1

8. A train approaching a railway platform with a speed of 20 ms1starts blowing the whistle. Speed of sound in air is 340ms1. If the frequency of the emitted sound from the whistle is 640 Hz, the frequency of sound to a person standing on

the platform will appear to be

(A) 600 Hz (B) 640 Hz (C) 680 Hz (D) 720 Hz

Ans : (C)

Hints : a 0s

V 340n .n 640 680Hz

V V 320

9. A straight wire of length 2 m carries a current of 10 A. If this wire is placed in a uniform magnetic field of 0.15 T making

an angle of 45owith the magnetic field, the applied force on the wire will be

(A) 1.5 N (B) 3 N (C) 3 2 N (D)3

2N

Ans : (D)

Hints :o 3F i l B i lBsin 10 2 0.15 sin45 .N

2

10. What is the phase difference between two simple harmonic motions represented by 1x A sin t6

and x2= A

cos ( t)?

(A)6

(B)3

(C)2

(D)2

3

Ans : (B)

Hints : 1 2X A sin t ,X Asin t

6 22 1 t t

2 6=

311. Heat is produced at a rate given by H in a resistor when it is connected across a supply of voltage V. If now the

resistance of the resistor is doubled and the supply voltage is made V/3 then the rate of production of heat in the

resistor will be

(A) H/18 (B) H/9 (C) 6H (D) 18H

Ans : (A)

Hints :

22 2VV 1 V H3H ,H .

R 2R 18 R 18


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12. Two elements A and B with atomic numbers ZAand Z

Bare used to produce characteristic xrays with frequencies A

and B respectively. If ZA: ZB= 1 : 2, then A B will be

(A) 1 : 2 (B) 1 : 8 (C) 4 : 1 (D) 1 : 4

Ans : (D)

Hints : a(z b) , Ignoring screening effect (i.e. b=0),

2

A A

A B

Z 1Z 4

13. The de Broglie wavelength of an electron moving with a velocity c/2 (c = velocity of light in vacuum) is equal to the

wavelength of a photon. The ratio of the kinetic energies of electron and photon is

(A) 1 : 4 (B) 1 : 2 (C) 1 : 1 (D) 2 : 1

Ans : (A)

Hints :

22

e

1 c 1K m mc

2 2 8, e

e

h h 2h

cp mcm2

ne p kp=K.E. of photon

2hc mc

p 2

e

p

k 1

k 4

14. Two infinite parallel metal planes, contain electric charges with charge densities + and respectively and they are

separated by a small distance in air. If the permittivity of air is 0 then the magnitude of the field between the two

planes with its direction will be

(A) / 0 towards the positively charged plane (B) / 0 towards the negatively charged plane

(C) /(2 0 ) towards the positively charged plane (D) 0 and towards any direction

Ans : (B)

15. A box of mass 2 kg is placed on the roof of a car. The box would remain stationary until the car attains a maximum

acceleration. Coefficient of static friction between the box and the roof of the car is 0.2 and g = 10 ms2.

This maximum acceleration of the car, for the box to remain stationary, is

(A) 8 ms2 (B) 6 ms2 (C) 4 ms2 (D) 2 ms2

Ans : (D)

Hints : amax

=g =0.210 = 2 m/s2

16. The dimension of angular momentum is

(A) M0L1T1 (B) M1L2T2 (C) M1L2T1 (D) M2L1T2

Ans : (C)Hints : [L]= [m r v] = [M1L2T1]

17. if A B C and A,B,C have scalar magnitudes of 5, 4 , 3 units respectivley then the angle between A and C is

(A) cos1(3/5)

(B) cos1(4/5)

(C) /2

(D) sin1 (3/4)

Ans : (A)

Hints :13 3Cos ; Cos

55

18. A particle is travelling along a straight line OX. The distance x (in meters) of the particle from O at a time t is given by

x = 37 + 27 t t 3where t is time in seconds. The distance of the particle from O when it comes to rest is

(A) 81 m (B) 91 m (C) 101 m (D) 111 m

Ans : (B)

Hints :2dxv 27 3t 0

dt, t = 3 sec. x = 37 + 273 33, = 37 + 81 27 = 91 m


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19. A particle is projected from the ground with kinetic energy E at an angle of 600with the horizontal. Its kinetic energy

at the highest point of its motion will be

(A) E / 2 (B) E / 2 (C) E / 4 (D) E / 8

Ans : (C)

Hints :2 o 2 2

i f

1 1 1 1 EK E mu ,K E m(ucos60 ) mu

2 2 2 4 4

20. A bullet on penetrating 30 cm into its target loses its velocity by 50%. What additional distance will it penetrate into

the target before it comes to rest?

(A) 30 cm (B) 20 cm (C) 10 cm (D) 5 cm

Ans : (C)

Hints :

2 2 22 2V V VV 2a(0.3)..........(1), 0 2as a ..............(2)

2 4 8s From (1) and (2) s = 10 m

21. When a spring is stretched by 10 cm, the potential energy stored is E. When the spring is stretched by 10 cm more,

the potential energy stored in the spring becomes

(A) 2 E (B) 4 E (C) 6 E (D) 10 E

Ans : (B)

Hints :20 0

1E kx ,x 10cm2

21E kx2

, x = 10 + 10= 20 cm = 2 x0

20

1k(2x ) 4E

222. Average distance of the earth from the Sun is L

1. If one year of the Earth = D days, one year of another planet whose

average distance from the Sun is L2will be

(A)

1

22

1

LD

Ldays (B)

3

22

1

LD

Ldays (C)

2

32

1

LD

Ldays (D)

2

1

LD

L days

Ans : (B)

Hints :

3 3

2 22 3 2 2 2

21 1 1

T L LT L D D

T L L

23. A spherical ball A of mass 4 kg, moving along a straight line strikes another spherical ball B of mass 1 kg at rest.

After the collision, A and B move with velocities v1ms1and v

2ms1respectively making angles of 30oand 60owith

respect to the original direction of motion of A. The ratio1

2

v

v will be

(A)3

4(B)

4

3(C)

1

3(D) 3

Ans : (A)

Hints : Apply conservation of momentum along Normal

m1V

1sin 30o= m

2V

2sin 60o

1

2

V 3

V 4

24. The decimal number equivalent ot a binary number 1011001 is

(A) 13 (B) 17 (C) 89 (D) 178

Ans : (C)

Hints : (1011001)2= 126+ 025 +124+ 123+ 022+ 021+ 120 = 64 + 16 + 8 + 1 =89


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25. The frequency of the first overtone of a closed pipe of length l1is equal to that of the first overtone of an open pipe of

length l2. The ratio of their lenghts (l

1: l

2) is

(A) 2 : 3 (B) 4 : 5 (C) 3 : 5 (D) 3 : 4

Ans : (D)

Hints :1

1 2 2

l3 2v 3.v

4l 2l l 426. The I V characteristics of a metal wire at two different temperatures (T

1and T

2) are given in the adjoining figure. Here,

we can conclude that

(A) T1> T

2(B) T

1< T

2(C) T

1= T

2(D) T

1= 2T

2

Ans : (B)

Hints :I 1

V R= slope of curve, R T greater the slope smaller will be temperature. T1< T2.

27. In a slide calipers, (m + 1) number of vernier divisions is equal to m number of smallest main scale divisions. If d unit

is the magnitude of the smallest main scale division, then the magnitude of the vernier constant is

(A) d/(m+1) unit (B) d/m unit (C) md/(m+1) unit (D) (m+1)d/m unit

Ans : (A)

Hints :m d

L.C 1 dm 1 m 1

28. From the top of a tower, 80 m high from the ground, a stone is thrown in the horizontal direction with a velocity of 8

ms1. The stone reaches the ground after a time t and falls at a distance of d from the foot of the tower. Assuming

g = 10 ms2, the time t and distance d are given respectively by

(A) 6 s, 64 m (B) 6 s, 48 m (C) 4 s, 32 m (D) 4 s, 16 m

Ans : (C)

Hints : time of flight (t) =2h 2 80

4s x 8 4 32mg 10

29. A Wheatstone bridge has the resistances 10 , 10 , 10 and 30 in its four arms. What resistance joined in parallel

to the 30 resistance will bring it to the balanced condition?

(A) 2 (B) 5 (C) 10 (D) 15

Ans : (D)

Hints : for a balanced bridge. R = 10 , 30 x 10 30x 300 10x 20x 300, x 1530 x

30. An electric bulb marked as 50 W200 V is connected across a 100 V supply. The present power of the bulb is

(A) 37.5 W (B) 25 W (C) 12.5 W (D) 10 W

Ans : (C)

Hints : Pactual consume

=

2 2

sr

r

V 100 50P 50 12.5 W

V 200 4


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Q. 31 - Q. 40 carry two marks each

31. A magnetic needle is placed in a uniform magnetic field and is aligned with the field. The needle is now rotated by an

angle of 600and the work done is W. The torque on the magnetic needle at this poition is

(A) 2 3 W (B) 3 W (C)3

2W (D)

3

4W

Ans : (B)

Hints :o MBW MB(1 cos ) MB(1 cos60 )

2,

o MBMBsin MBsin 60 3 3W2

32. In the adjoining figure the potential difference between X and Y is 60 V. The potential difference between the points M

and N will be

(A) 10 V (B) 15 V (C) 20 V (D) 30 V

Ans : (D)

Hints :eq net MN

190C

C C 3C C 3 , q 90C V 30V2 2 C

33. A body when fully immersed in a liquid of specific gravity 1.2 weighs 44 gwt. The same body when fully immersed in

water weighs 50 gwt. The mass of the body is

(A) 36 g (B) 48 g (C) 64 g (D) 80 g

Ans : (D)

Hints : mg vg = 44, = density of liquid, mg 1.2 vg = 44 ..............(1), = density of water

mg vg = 50.............(2), (1) 1.2(2) M = 80 g

34. When a certain metal surface is illuminated with light of frequency , the stopping potential for photoelectric current

is V0. When the same surface is illuminated by light of frequency

2, the stopping potential is 0

V

4. The threshold

frequency for photoelectric emission is

(A)6

(B)3

(C)2

3(D)

4

3

Ans : (B)

Hints : e V0= h

0.........(1), 0

eV

4

h

2

0.........(2), solving equation (1) and (2) , 0

3

35. Three blocks of mass 4 kg, 2 kg, 1 kg respectively are in contact on a frictionless table as shown in the figure. If a

force of 14 N is applied on the 4 kg block, the contact force between the 4 kg block, the contact force between the 4

kg and the 2 kg block will be

(A) 2 N (B) 6 N (C) 8 N (D) 14 N

Ans : (B)

Hints :2net

net

F 14a 2m / s R 3 2 6N

m 7


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36. Let L be the length and d be the diameter of cross section of a wire. Wires of the same material with different L and

d are subjected to the same tension along the length of the wire. In which of the following cases, the extension of wire

will be the maximum?

(A) L = 200 cm, d = 0.5 mm (B) L = 300 cm, d = 1.0 mm

(C) L = 50 cm, d = 0.05 mm (D) L = 100 cm, d = 0.2 mm

Ans : (C)

Hints :TL L

L LAY A

37. An object placed in front of a concave mirror at a distance of x cm from the pole gives a 3 times magnified real image.

If it is moved to a distance of (x + 5) cm, the magnif ication of the image becomes 2. The focal length of the mirror is

(A) 15 cm (B) 20 cm (C) 25 cm (D) 30 cm

Ans : (D)

Hints : 1uf ( x)( f) 4

v ,v 3x x f.........(1)u f x f 3

, 2(x 5)( f )

v , 2x 10 3f x 5 f

.............(2)

so f = 30 cm

38. 22320 cal of heat is supplied to 100 g of ice at 0oC. If the latent heat of fusion of ice is 80 cal g1and latent heat of

vaporization of water is 540 cal g1, the final amount of water thus obtained and its temperature respectively are

(A) 8g, 100oC (B) 100 g, 90oC (C) 92g, 100oC (D) 82g, 100oC

Ans : (C)

Hints : total energy required to melt and boil at 100oC is

(Q)min

= 8000 + 10000 = 18000 cal, (Qrequired

)min

< Qgiven

for amount of vapour 22320=18000+ m 540

m = 8 gm. temperature = 100oC and water remaining = 92 gm.

39. A progressive wave moving along xaxis is represented by2

y A sin t x . The wavelength ( ) at which the

maximum particle velocity is 3 times the wave velocity is

(A) A / 3 (B) 2A / (3 ) (C) (3/4) A (D) (2/3) A

Ans : (D)

Hints :2 2

A 3 A3

40. Two radioactive substances A and B have decay constant 5 and respectively. At t = 0, they have the same number

of nuclei the ratio of number of nuclei of A to that of B will be (1/e)2after a time interval of

(A)1

(B)1

2(C)

1

3(D)

1

4

Ans : (B)

Hints :

5 t1

t 22

N e 1 1, t

N 2e e

Q. 41 - Q. 70 carry one mark each

41. Li occupies higher position in the electrochemical series of metals as compared to Cu since

(A) the standard reduction potential of Li+/Li is lower than that of Cu2+/Cu

(B) the standard reduction potential of Cu2+/Cu is lower than that of Li+/Li

(C) the standard oxidation potential of Li/Li+is lower than that of Cu/Cu2+

(D) Li is smaller in size as compared to Cu

Ans : (A)

Hints : ELi

+/Li

= 3.04V ; ECu

2+/Cu

= 0.34V


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42.11

Na24is radioactive and it decays to

(A)9F20and -particles (B)

13Al24and positron (C)

11Na23and neutron (D)

12Mg24and -particles

Ans : (D)

Hints :2424 01211 1Na Mg e

(n/p = 1.18) (n/p=1)

43. The paramagnetic behavior of B2is due to the presence of

(A) 2 unpaired electrons inbMO (B) 2 unpaired electrons in MO

(C) 2 unpaired electrons in MO (D) 2 unpaired electrons inbMO

Ans : (A)

Hints :_

2 *2 2 *22 1s 1s 2s 2 sB (10 e )

44. A 100 ml 0.1 (M) solution of ammonium acetate is diluted by adding 100 ml of water. The pH of the resulting solution

will be (pKaof acetic acid is nearly equal to pK

bof NH

4OH)

(A) 4.9 (B) 5.0 (C) 7.0 (D) 10.0

Ans : (C)

Hints : Hydrolysis of a salt of weak acid and weak base

pH = 7 + (pKa pK

b) = 7 a b[ pK pK ]

45. In 2-butene, which one of the following statements is true ?

(A) C1-C

2bond is a sp3- sp3 -bond (B) C

2-C

3bond is a sp3- sp2 -bond

(C) C1-C

2bond is a sp3- sp2 -bond (D) C

1-C

2bond is a sp2- sp2 -bond

Ans : (C)

Hints :

But-2-ene

46. The well known compounds, (+)- lactic acid and () lactic acid have the same molecular formula, C3H

6O

3. The correct

relationship between them is

(A) constitutional isomerism (B) geometrical isomerism (C) identicalness (D) optical isomerism

Ans : (D)

Hints :

They are enantiomers and correct relationship between them is optical isomerism.

47. The stability of Me2C=CH

2is more than that of MeCH

2CH = CH

2due to

(A) inductive effect of the Me group (B) resonance effect of the Me group

(C) hyperconjugative effect of the Me group (D) resonance as well as inductive effect of the Me group

Ans : (C)

Hints : Me2C = CH

2is more stable than MeCH

2CH = CH

2due to hyperconjugative effect.

(6 number of H) (2 number of H)


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48. Which one of the following characteristics belongs to an electrophile ?

(A) It is any species having electron deficiency, which reacts at an electron rich C-centre

(B) It is any species having electron enrichment that reacts at an electron deficient C-centre

(C) It is cationic in nature

(D) It is anionic in nature

Ans : (A)

Hints : Fact

49. Which one of the following methods is used to prepare Me3COEt with a good yield?

(A) Mixing EtONa with Me3CCl

(B) Mixing Me3CONa with EtCl

(C) Heating a mixture of (1:1) EtOH and Me3COH in presence of conc. H

2SO

4

(D) Treatment of Me3COH with EtMgl

Ans : (B)

Hints :3

+

3

3

+ CH3CH

2Cl NS 2

3 2 3

3

3

Williamsons synthesis (SN2) given by 1 alkyl halide.

50. 58.5 gm of NaCl and 180 gm of glucose were separately dissolved in 1000 ml of water. Identify the correct statement

regarding the elevation of boiling point (b.p.) of the resulting solutions.

(A) NaCl solution will show higher elevation of b.p.

(B) Glucose solution will show higher elevation of b.p.

(C) Both the solutions will show equal elevation of b.p.

(D) The b.p. elevation will be shown by neither of the solutions

Ans : (A)

Hints : For NaCl (i = 2) for glucose (i = 1),

Hence NaCl solution will show higher elevation of bp (Colligative property) as both are one Molar Solution.

51. Equal weights of CH4and H

2are mixed in an empty container at 25oC. The fraction of the total pressure exerted by H

2

is

(A) 1/9 (B) 1/2 (C) 8/9 (D) 16/17

Ans : (C)

Hints : Let equal weights be w g.

mole fraction of 2w / 2

Hw / 2 w / 16 9

Partial pressure = mole fraction Total pressure

2H

8p

9 Total Pressure

52. Which of the following will show a negative deviation from Raoults law?

(A) Acetone-benzene (B) Acetone-ethanol(C) Benzene-methanol (D) Acetone-chloroform

Ans : (D)

Hints :Acetone chloroform due to formation of intermolecular Hydrogen bonding


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53. In a reversible chemical reaction at equilibrium, if the concentration of any one of the reactants is doubled, then the

equilibrium constant will

(A) also be doubled (B) be halved

(C) remain the same (D) become one-fourth

Ans : (C)

Hints : Equilibrium constant does not depend on conc. It is only a function of temperature

54. Identify the correct statement from the following in a chemical reaction.

(A) The entropy always increases

(B) The change in entropy along with suitable change in enthalpy decides the fate of a reaction

(C) The enthalpy always decreases

(D) Both the enthalpy and the entropy remain constant

Ans : (B)

Hints : Spontaneity of a reaction is decided by a combined effect of suitable change in values of enthalpy and

entropy. [ G = H T S]

55. Which one of the following is wrong about molecularity of a reaction?

(A) It may be whole number or fractional

(B) It is calculated from reaction mechanism

(C) It is the number of molecules of the reactants taking part in a single step chemical reaction

(D) It is always equal to the order of elementary reaction

Ans : (A)

Hints : Molecularity can never be a fraction.

56. Which of the following does not represent the mathematical expression for the Heisenberg uncertainty principle?

(A) x. p h/(4 ) (B) x. v h/(4 m) (C) E. t h/(4 ) (D) E. x h/(4 )

Ans : (D)

Hints : Fact.

57. The stable bivalency of Pb and trivalency of Bi is

(A) due to d contraction in Pb and Bi

(B) due to relativistic contraction of the 6s orbitals of Pb and Bi, leading to inert pair effect

(C) due to screening effect

(D) due to attainment of noble liquid configuration

Ans : (B)

Hints : Lower oxidation state becomes more stable for group 14 and group 15 elements as we move down the group

due to inert pair effect. Hence Pb+2and Bi+3are more stable.

58. The equivalent weight of K2Cr

2O

7in acidic medium is expressed in terms of its molecular weight (M) as

(A) M/3 (B) M/4 (C) M/6 (D) M/7

Ans : (C)

Hints : Cr2O

72+ 14H++ 6e 2Cr+3+ 7H

2O

Number of electrons gained by one ion = 6

Eq.wt

M

6

59. Which of the following is correct ?

(A) radius of Ca2+< Cl-< S2- (B) radius of Cl-< S2-< Ca2+

(C) radius of S2-= Cl-= Ca2+ (D) radius of S2-< Cl-< Ca2+

Ans : (A)

Hints : Ca+2, S2, Cl are isoelectronic (consist of 18e) and for isoelectronic species, ionic radiie

z


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60. CO is practically non-polar since

(A) the -electron drift from C to O is almost nullified by the -electron drift from O to C

(B) the -electron drift from O to C is almost nullified by the -electron drift from C to O

(C) the bond moment is low

(D) there is a triple bond between C and O

Ans : (A)

Hints : Factual

61. The number of acidic protons in H3PO

3are

(A) 0 (B) 1 (C) 2 (D) 3

Ans : (C)

Hints : Number of OH group is 2 hence dibasic in nature.

62. When H2

O2

is shaken with an acidified solution of K2

Cr2

O7

in presence of ether, the ethereal layer turns blue due to

the formation of

(A) Cr2O

3(B) CrO

42- (C) Cr

2(SO

4)3

(D) CrO5

Ans : (D)

Hints : K2Cr

2O

7+ H

2SO

4 + 4H

2O

2ether 2CrO

s+ K

2SO

4+ 5H

2O

(Blue)

63. The state of hybridization of the central atom and the number of lone pairs over the central atom in POCl3are

(A) sp, 0 (B) sp2, 0 (C) sp3, 0 (D) dsp2, 1

Ans : (C)

Hints : Number of lone pairs on P atom = 0

64. Upon treatment with l2and aqueous NaOH, which of the following compounds will form iodoform?

(A) CH3CH

2CH

2CH

2CHO (B) CH

3CH

2COCH

2CH

3

(C) CH3CH

2CH

2CH

2CH

2OH ( D) CH

3CH

2CH

2CH(OH)CH

3

Ans : (D)

Hints : Iodoform reaction is given by all alcohols having .

65. Upon treatment with Al(OEt)3

followed by usual reactions (work up), CH3

CHO will produce

(A) only CH3COOCH

2CH

3(B) a mixture of CH

3COOH and EtOH

(C) only CH3COOH (D) only EtOH

Ans : (A)

Hints : 3Al(OEt)CH COCH CH

O

This reaction is known as Tischenko reaction


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66. Friedel-Crafts reaction using MeCl and anhydrous AlCl3will take place most efficiently with

(A) Benzene (B) Nitrobenzene (C) Acetophenone (D) Toluene

Ans : (D)

Hints : As CH3group in toluene activates the benzene ring for electrophilic substitution reaction.

67. Which one of the following properties is exhibited by phenol?

(A) It is soluble in aq. NaOH and evolves CO2

with aq. NaHCO3

(B) It is soluble in aq. NaOH and does not evolve CO2with aq. NaHCO

3

(C) It is not soluble in aq. NaOH but evolves CO2with aq. NaHCO

3

(D) It is insoluble in aq. NaOH and does not evolve CO2with aq. NaHCO

3

Ans : (B)

Hints :

+

+

2 (Soluble in aqueous NaOH)

Phenol is less acidic than H2CO

3. So it cannot liberate CO

2from NaHCO

3(aq).

68. The basicity of aniline is weaker in comparison to that of methyl amine due to

(A) hyperconjugative effect of Me-group in MeNH2

(B) resonance effect of phenyl group in aniline

(C) lower molecular weight of methyl amine as compared to that of aniline

(D) resonance effect of NH2group in MeNH

2

Ans : (B)

Hints :

2 2

+

Here delocalisation of lone pair of nitrogen.

23No delocalisation of lone pair

69. Under identical conditions, the SN1 reaction will occur most efficiently with

(A) tert-butyl chloride (B) 1-chlorobutane

(C) 2-methyl-1-chloropropane (D) 2-chlorobutane

Ans : (A)

Hints : Reactivity order for SN1 reaction in case of alkyl halide is 3> 2> 1

70. Identify the method by which Me3CCO

2H can be prepared

(A) Treating 1 mol of MeCOMe with 2 moles of MeMgl (B) Treating 1 mol of MeCO2Me with 3 moles of MeMgl

(C) Treating 1 mol of MeCHO with 3 moles of MeMgl (D) Treating 1 mol of dry ice with 1 mol of Me3CMgl

Ans : (D)

Hints : Reaction+ +


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Q. 71 to Q. 80 carry two marks each.

71. 20 ml 0.1 (N) acetic acid is mixed with 10 ml 0.1 (N) solution of NaOH. The pH of the resulting solution is (pKaof acetic

acid is 4.74)

(A) 3.74 (B) 4.74 (C) 5.74 (D) 6.74

Ans : (B)

Hints : CH3COOH + NaOH CH

3COONa + H

2O

Initial 20 ml 0.1N 10ml 0.1N 0 meq

= 2 meq = 1 meq

Final 1 meq 0 meq 1 meq

Mixed solution behaves as acidic buffer

a

[Salt]pH pK log

[Acid]= 4.74 + log

1

1= 4.74

72. In the brown ring complex [Fe(H2O)5(NO)]SO4, nitric oxide behaves as

(A) NO+ (B) neutral NO molecule (C) NO (D) NO2

Ans : (A)

Hints : NO ligand when attached to Fe behaves as positively charged ligand.

73. The most contributing tautomeric enol form of MeCOCH2CO

2Et is

(A) CH2= C(OH)CH

2CO

2Et (B) MeC(OH) = CHCO

2Et

(C) MeCOCH = C(OH)OEt (D) CH2= C(OH)CH = C(OH) OEt

Ans : (B)

Hints :

74. By passing excess Cl2(g) in boiling toluene, which one of the following compounds is exclusively formed?

(A) (B) (C)

3

(D)

3

Ans : (D)

Hints :Free Radical

benzylic substitution


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75. An equimolar mixture of toluene and chlorobenzene is treated with a mixture of conc. H2SO

4and conc. HNO

3.

Indicate the correct statement from the following

(A) p-nitrotoluene is formed in excess

(B) equimolar amounts of p-nitrotoluene and p-nitrochlorobenzene are formed

(C) p-nitrochlorobenzene is formed in excess

(D) m-nitrochlorobenzene is formed in excess

Ans : (A)

Hints :

CH3is activating group due to +I effect and hyperconjugation.

But for Cl, I > + R effect.

CH3is weakly activating and Cl is weakly deactivating76. Among the following carbocations : Ph

2C+CH

2Me(I), PhCH

2CH

2CH+Ph (II), Ph

2CHCH+Me (III) and Ph

2C(Me)CH

2+(IV),

the order of stability is

(A) IV > II > I > III (B) I > II > III > IV (C) II > I > IV > III (D) I > IV > III > II

Ans : (B)

Hints :

Number of resonating structures decide stability in I and II.

77. Which of the following is correct?

(A) Evaporation of water causes an increase in disorder of the system

(B) Melting of ice causes a decrease in randomness of the system

(C) Condensation of steam causes an increase in disorder of the system

(D) There is practically no change in the randomness of the system when water is evaporated

Ans : (A)

Hints : Evaparation increases randomness as liquid water is converted to water vapours.

78. On passing C Ampere of current for time t sec through 1 litre of 2 (M) CuSO4solution (atomic weight of Cu = 63.5),

the amount m of Cu (in gm) deposited on cathode will be

(A) m = Ct / (63.5 96500) (B) m = Ct/ (31.25 96500)

(C) m = (C 96500) / (31.25 t) (D) m = (31.25 C t) / 96500

Ans : (D)

Hints : 1000 ml 2(M) CuSO4

2(M) CuSO4solution contains 2 moles Cu+2

Cu2+ 2e Cu

2F 63.5g q = c t coulomb

or, 2 96500C

63.5 31.25 Ctm Ct g

2 96500 96500


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79. If the 1stionization energy of H atom is 13.6 eV, then the 2ndionization energy of He atom is

(A) 27.2 eV (B) 40.8 eV (C) 54.4 eV (D) 108.8 eV

Ans : (C)

Hints : H 213.6

En

1 HE 13.6eV

1 HeE

2

2

z13.6n

2213.61

= 54.4eV

The 2ndIE = E 1 HeE = 0 (54.4) eV = 54.4 eV

80. The weight of oxalic acid that will be required to prepare a 1000 ml (N/20) solution is

(A) 126/100 gm (B) 63 / 40 gm (C) 63 / 20 gm (D) 126 / 20 gm

Ans : (C)

Hints : M.wt. of H2C

2O

4. 2H

2O is 126 (n.factor = 2) , E.wt =

126

2= 63

no. of gm equivalentN

volume of solution inL

1 w / 63 63w gm

20 1 20

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