Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

In BF3, the B - F bond length is 1.30Å, when BF3 is allowed to be treated with Me3N, it forms an adduct, Me3N BF3, the bond length of B - F in the adduct is

  • greater than 1.30 Å

  • smaller than 1.30 Å

  • equal to 1.30 Å

  • none of these


A.

greater than 1.30 Å

In BF3, there is back bonding in between fluorine and boron due to presence of p-orbital in boron. Back bonding imparts double bond characteristics.

As BF, forms adduct the back bonding is no longer present and thus double bond characteristic disappears. Hence, bond becomes a bit longer than earlier (1.30 Å).


2.

Which of the following is most basic?

  • Al(OH)3

  • Cr(OH)3

  • La(OH)3

  • Fe(OH)3


C.

La(OH)3

La(OH)3 is the most basic as it has the largest atomic size. Al(OH)3 is amphoteric in nature.


3.

Which thermodynamic parameter is not a state function?

  • q at constant pressure

  • q at constant volume

  • W at adiabatic

  • W at isothermal


D.

W at isothermal

and are state functions but W and q are not state functions.

From the equation, H = U + PV

At constant pressure, H = U + PV

At constant volume, H = U + VP

At constant pressure, P = 0, H = qp

so, it is a state function.

At constant volume, V = 0, U = qv

so, it is a state function.

Work done in any adiabatic process is state function.

U = q - W ( q = 0)

U = -W

Work done in isothermal process is not a state function.

W = -q ( T = 0, q 0)


4.

Maximum number of unpaired electrons are present in

  • Gd3+

  • Yb2+

  • Tb2+

  • Pm3+


A.

Gd3+

Maximum number of unpaired electrons are present in Gd3+. It has 7 unpaired electrons.

Yb2+ has no unpaired electrons.

Tb2+ has 5 unpaired electrons.

Pm3+ has 4 unpaired electrons.


5.

Assertion : Bond dissociation energy is F2 > Cl2.

Reason : Cl2 has more electronic repulsion than F2.

  • If both assertion and reason are true and reason is the correct explanation of assertion.

  • If both assertion and reason are true but reason is not the correct explanation of assertion.

  • If assertion is true but reason is false.

  • If both assertion and reason are false.


D.

If both assertion and reason are false.

Bond dissociation energy is F2 < Cl2 because of relatively large electron-electron repulsion among the lone pairs in F2 molecule where they are much closer to each other
than in Cl2.


6.

K2Cr2O7 in acidic medium converts into

  • Cr2+

  • Cr3+

  • Cr4+

  • Cr5+


B.

Cr3+

K2Cr2O7 in acidic medium converts into Cr3+. Since it is an oxidising agent, it undergoes reduction, i.e. decrease in oxidation state.

Cr2O72- + 14H+ + 6e- 2Cr3+ + 7H2O


7.

Total number of antibonding electrons present in O2 will be

  • 6

  • 8

  • 4

  • 2


A.

6

Total number of antibonding electrons present in O2 is 6.

(σ1s)2(σ*1s)2(σ2s)2(σ*2s)2(σ2pz)2(π2px2 = π2py2)(π*2px1 = π*2py1)


8.

Which of the following element has lowest melting point?

  • Cr

  • Fe

  • Ni

  • Cu


D.

Cu

Cu has lowest melting point because it has lowest enthalpy of atomisation (i.e., heat required to break the metal lattice to get free atoms) among the elements.


9.

A particle is moving 3 times faster than the speed of electron. If the ratio of wavelength of particle and electron is 1.8 x 10-4 then particle is

  • neutron

  • α- particle

  • deuteron

  • tritium


A.

neutron

Given : λparticleλelectron = 1.8 × 10-4

and νparticleνelectron = 3

According to de-Brogile equation, λ = h

λparticleλelectron = hmparticle × νparticle × melectron × νelectronh                 = melectronmparticle × νelectronνparticle

 1.8 × 10-4 = 9.1 × 10-31 kgmparticle × 13mparticle = 9.1 × 10-311.8 × 10-4 × 3 = 1.6852 × 10-27 kg

Actual mass of neutron is 1.67493 × 10-27 kg. Hence, the particle is neutron.


10.

What will be the solubility product of AX3?

  • 27S4

  • 4S3

  • 36S4

  • 9S3


A.

27S4

AX3  A3+S + 3X-3S

Ksp = [A3+] [X-]3

      = (S).(3S)3 = 27S4