Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

Assertion : Molecular nitrogen is less reactive than molecular oxygen.

Reason : The bond length of N2 is shorter than that of oxygen.

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

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

  • If assertion is true, but reason is false.

  • Both assertion and reason are false statements.


A.

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

Bond order of N2= 3, bond order of O2= 2. Higher the bond order, higher is the bond dissociation energy. i.e. higher stability or less reactivity. Thus N2 is less reactive than O2. Higher the bond order, shorter is the bond length. Shorter bond length of N2 shows its higher bond order.


2.

The enthaply change (H) for the reaction

       N2(g) + 3H2(g) 2NH3(g)

is -92.38 kJ at 298K . The internal energy change U at 298K is

  • -92.38 kJ

  • -87.42 kJ

  • -97.34 kJ

  • -89.9 kJ


B.

-87.42 kJ

H=U+nRT[where n= no.of molecules of product - no.of molecules of reactants]or,-92.38 ×1000=U-2×8.314×298or,U=-87424 J=-87.424kJ


3.

Dominance of strong repulsive forces among the molecules of the gas (Z = compressibility factor)

  • depends on Z and indicated by Z = 1

  • depends on Z and indicated by Z > 1

  • depends on Z and indicated by Z < 1

  • is independent of Z.


B.

depends on Z and indicated by Z > 1

When the value of Z < 1, it is due to attractive forces between molecules. At high pressure, when Z> 1, it is due to repulsive forces between electron clouds of the molecules of gases.


4.

The de Broglie wavelength associated with a ball of mass 1kg having kinetic energy 0.5 J is

  • 6.626 × 10-34 m.

  • 13.20 × 10-34 m.

  • 10.38 × 10-21m.

  • 6.626 ×10-34A°.


A.

6.626 × 10-34 m.

Kinetic energy =12mv2 [m= mass, v= velocity]

or, 0.5=12×1×v2 or, v=1 ms-1

de Brogile wavelength, λ=hmv

or, λ=6.626 × 10-34 Js1 kg × 1 ms-1= 6.626 ×10-34m.


5.

For a phase change

H2O(l)   0°C, 1 bar  H2O(s)

  • G = 0

  • H = 0

  • S =0

  • U = 0


A.

G = 0

G°=-RTlnK  [G°= standard free energy change, K = equilibrium constant]

If a substance is in equilibrium between two phases at constant temperature and pressure, its chemical potential must have the same value in both the phases. Therefore G°=0.


6.

Assertion : Water in liquid state is more stable than ice at room temperature.

Reason : Water in liquid form has higher entropy than ice.

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

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

  • If assertion is true, but reason is false.

  • Both assertion and reason are false statements.


A.

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

Fusion of ice is a spontaneous process, because the process again proceeds in the direction of more random state, i.e. liquid state is more random (higher entropy) in comparison to solid state. i.e., ice.


7.

Among the following, the species having square planar geometry for central atom are
(i) XeF4, (ii) SF4, (iii) [NiCl4]2- ,(iv) [PdCl]2-

  • (i) and (iv)

  • (i) and (ii)

  • (ii) and (iii)

  • (iii) and (iv).


A.

(i) and (iv)

XeF: sp3 dhybridisation, shape is square planar instead of octahedral due to presence of two lone pair of electrons on Xe atom. SF4: SF4 molecule shows sp3d hybridisation but its expected trigonal bipyramidal geometry gets distorted due to presence of a lone pair of electrons and it becomes distorted tetrahedral or see-saw with the bond angles equal to 89° and 177° instead of the expected angles of 90° and 180° respectively.

Experiments have, however, shown that 4-coordinated complexes of Pd(II) are diamagnetic (n = 0). Thus it is dsphybridisation which is involved in the formation of (PdCl4]2- ion i.e. 4-coordinated complexes of Pd(II) have square planar geometry with n = 0 (diamagnetic).

 

 


8.

Borax is used as a cleansing agent because on dissolving in water it gives

  • alkaline solution

  • acidic solution

  • bleaching solution

  • basic solution.


A.

alkaline solution

Borax dissolves in water to give alkaline solutions.

Na2B4O7 + 2H2O 2NaOH  strong base+ H3BO3weak acid

Borax is therefore used as a water softener and cleansing agent.


9.

40 mL of 0.1 M ammonia solution is mixed with 20 mL. of 0.1 M HCl. What is the pH of the mixture? (pKb, of ammonia solution is 4.74)

  • 4.74

  • 2.26

  • 9.26

  • 5.00


C.

9.26

40 mL of 0.1 M ammonia solution= 40 x 0.1 = 4 milliequivalent ammonia solution.

20 mL. of 0.1M HCl =20 x 0.1 =2 milli equivalent of HCl

                       NH4OH + HCl   NH4Cl + H2O

Initial milli-eqv.     4        2           0

Milli-eqv. after     4-2       0           2

                          =2

pOH = pKb + log[NH4Cl][NH4OH]=4.72 + log22         = 4.74 + log 1= 4.74   pH = 14- 4.74 =9.26


10.

For a spontaneous process the correct statement is

  • entropy of the system always increases.

  • free energy of the system always increases.

  • total entropy change is always negative.

  • total entropy change is always positive.


D.

total entropy change is always positive.

Stotal = Ssystem+ Ssurroundings

For a spontaneous process Stotal must be positive. i.e. Stotal >0.