Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

At 27°C, one mole of an ideal gas is compressed isothermally and reversibly from a pressure of 2 atm to 10 atm. Choose the correct option from the following

  • Change in internal energy is positive

  • Heat is negative

  • Work done is - 965.84 cal

  • All are incorrect


B.

Heat is negative

Work done in isothermal reversible process is 

w = -2.303 nRT log10p1p2

Given, n = 1; R = 2 cal K-1 mol-1

T = (27 + 273) K = 300 K

p1 = 2 atm; p2 = 10 atm

Therefore,

w = -2.303 × 1 × 2 × 300 log10210 

w = + 965.54 cal

For isothermal change, U = 0

Now, from first law of thermodynamics,

q = U - w = 0 - 965.84 cal

q = -965.84 cal


2.

Choose the correct statement from the following

  • NH4+ and CH4 are not isoelectronic species

  • BF3 does not have dipole moment

  • O - Cl - O obeys octet rule

  • O- in O3 is Sp3-hybridised


B.

BF3 does not have dipole moment

Among all the given statements, statement b is correct. Other statements can be corrected as-

a. For NH4+, number of valance electrons = 10

For CH4, number of valance electrons = 10.

They both are isoelectronic species.

c. O - Cl - O does not follow octet rule.

d. O- in O3 is sp2- hybridised.


3.

The melting point of solid substances is directly proportional to pressure acting on them. However, ice-melts at a temperature lower than its usual melting point, when the pressure increases. This is because

  • ice is not a true solid

  • the bonds break under pressure

  • ice is less denser than water

  • pressure generates heat


C.

ice is less denser than water

For most substances, increasing the pressure when a system is in equilibrium between liquid and solid phases will increase the phase transition temperature. Ice melts at a temperature lower than its usual melting point because ice is less denser than water.


4.

Work is being performed, when a weight lifter lifts a base ball off a weight rack. This is due to

  • magnetic attraction

  • gravity

  • electrostatic repulsion

  • mechanical force


B.

gravity

Due to gravity, barbell is lifed and hence work is done.


5.

Choose the incorrect statement about noble gas?

  • Boiling point increases with increasing atomic mass

  • Helium has least tendency to form compound

  • Noble gases have some value of electron affinity

  • Xenon has maximum number of compounds


C.

Noble gases have some value of electron affinity

Noble gases make up a group of chemical elements with similar properties. These include helium, neon, argon, krypton, xenon and radon. 

Among all the given statements, statement c is incorrect. It can be corrected as valence shells of noble gases are complete, thus, they do not show tendency to gain electrons. Therefore, they have zero electron affinity.


6.

Temperature of a gas is t K. What would be the temperature at which volume and pressure, both will reduced to half of the initial values?

  • t2

  • t4

  • t3

  • t8


B.

t4

Given that,

p1 = p1T1 = t; V1 = v

p2p2; V2v2

T = ?

By using Boyle's law

p1V1T1 = p2V2T2

p × Vt = p × V2 × 2 ×T2

T2 = t4


7.

Beryllium differs in properties from other elements of its own group but shows resemblance with aluminium because of

  • relatively bigger ionic radius and high polarising power of Be

  • relatively smaller ionic radius and high polarising power of Be

  • relatively bigger ionic radius is the only reason behind this

  • None of the above


B.

relatively smaller ionic radius and high polarising power of Be

Beryllium or Be differs in properties from other elements of its own group but shows resemblance with aluminium because of its smaller ionic radius and high polarising power. Polarising powers of Be2+ and Al3+ ions are almost the same thus, they show similarities in their properties.


8.

What will be the number of waves formed by a Bohr electron in one complete revolution in its second orbit?

  • Three

  • Two

  • One

  • Zero


B.

Two

Number of waves = Number of wavesde- Brogile wavelength of electron

But, λ = hmv 

 λ = 2π3 × μh = 2πn × mvr

 mvr = nh2π = 2πh × nh2π

mvr = n

For second orbit, n = 2. Therefore, number of waves = 2.


9.

Aqueous solution of AlCl3 is acidic towards litmus while of NaCl is not. The correct reason behind this is

  • AlCl3, furnishes OH- ion in the solution

  • AlCl3, furnishes H+ ion in the solution

  • AlCl3, furnishes both H+ well as OH- ion in the solution

  • AlCl3, is the salt of strong base and strong acid


B.

AlCl3, furnishes H+ ion in the solution

AlCl3 is the salt of weak base and strong acid which renders H+ ions on hydrolysis. Thus, aqueous solution of AlCl3 is acidic in nature.

Al3+ + 3H2Al(OH)3 + 3H+

On the other hand, NaCl is the salt of strong acid and strong base which does not undergo hydrolysis.


10.

Which of the following pair of compounds will have three sp2 -hybrid orbitals?

  • SO2, CH4

  • SO3, C2H4

  • BF3, SF3

  • I3-, SF4


B.

SO3, C2H4

Among all the given pairs, second pair has sp2- hybrid orbitals.

SO2 is trigonal planar. It has 3 sp2- hybrid orbitals.

CH4 is tetrahedral. It has 4 sp3- hybrid orbitals.

SO3 and C2H4 are trigonalplanar and have 3 sp2- hybrid orbitals.

BF3 is trigonal planar. It also has 3 sp2- hybrid orbitals.

SF4 is irregular tetrahedral. It has 5 sp3d hybrid orbitals.

I3-L is linear and has 5 sp3d hybrid orbitals.