Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

Predict the correct order among the following.

  • long pair-lone pair> bond pair-bond pair> lone pair>bond pair

  • bond pair-bond pair> lone pair-bond pair > lone pair -lone pair

  • lone pair -bond pair > bond pair- bond pair> lone pair -lone pair

  • lone pair -bond pair > bond pair- bond pair> lone pair -lone pair


D.

lone pair -bond pair > bond pair- bond pair> lone pair -lone pair

According to the VSPER theory, a lone pair occupies more space than a bond pair, Hence when lone pair-lone pair interacts with each other they repel more and thus the correct order is:

lone pair - lone pair > lone pair-bond pair > bond pair -bond pair.

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2.

Two electrons occupying the same orbital are distinguished by

  • Magnetic quantum number

  • Azimuthal quantum number

  • Spin quantum number

  • Spin quantum number


C.

Spin quantum number

Two electrons occupying the same orbital has equal spin but the directions of their spin are opposite. Hence, spin quantum number, s(represented +1/2 and -1/2) distinguishes them.

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3.

In which of the following options the order of arrangement does not agree with the variation of the property indicated against it?

  • B<C<N<O (increasing first ionisation enthalpy)

  • I<Br<Cl<F(increasing electron gain enthalpy)

  • Li<Na<K<Rb (increasing metallic radius)

  • Li<Na<K<Rb (increasing metallic radius)


B.

I<Br<Cl<F(increasing electron gain enthalpy)

The electron gain enthalpy is defined as the energy released when an electron is added to a neutral gaseous atom to convert it into a negative ion. Large negative values of electron gain enthalpy indicate that it is easier to add an electron to an atom to convert it into an anion, and hence large amount of energy is released. The electron gain enthalpies in halogens decreases in the order
Cl>F>Br>I

because as we proceed down a group because the size of the atom increases. Therefore the distance of the nucleus from the valence orbital (which accepts the additional electron) increases. Hence the force by which the additional electron is attracted by the nucleus also decreases and the electron gain enthalpies become less negative as we proceed down a group.

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4.

Which one of the following characteristics is associated with adsorption?

  • ΔG, ΔH and  ΔS all are negative

  • ΔG and  ΔH are negative but  ΔS is positive

  • ΔG and  ΔS are negative but  ΔH is positive

  • ΔG and  ΔS are negative but  ΔH is positive


A.

ΔG, ΔH and  ΔS all are negative

Adsorption is a spontaneous process that occurs with the release of energy and decrease in the entropy of the substance. For a spontaneous process,  ΔG must be  negative,

 ΔG = ΔH - T ΔS

As the process is exothermic and randomness of the molecule (entropy) decreases hence both  ΔH and  ΔS will be negative as well.

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5.

The electronic configuration of Eu (Atomic no.63), Gd (Atomic no. 64) and Tb (Atomic no. 65) are

  • [Xe]4f6 5d1 6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9  6s2 

  • [Xe] 4f6 5d1 6s2 , [Xe] 4f7 5d1 6s2 and [Xe] 4f8 5d1 6s2 

  • [Xe] 4f7  6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2 

  • [Xe] 4f7  6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2 


C.

[Xe] 4f7  6s2, [Xe] 4f7 5d1 6s2 and [Xe] 4f9 6s2 

Electronic configuration of 63Eu [europium ]
= [Xe] 4f7  6s2

Electronic configuration of 64Gd [gadolinium ]
= [Xe] 4f7 5d1 6s2 

Electronic configuration 65Tb [terbium]
= [Xe] 4f9 6s2 

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6.

The pair of an electron in the given carbanion,CH subscript 3 straight C identical to straight C to the power of minus is present in which orbital? 

  • sp3

  • sp2

  • sp

  • sp


C.

sp

Hybridisation space equals space fraction numerator Number space of space straight sigma minus electrons over denominator 2 end fraction
space equals space fraction numerator 2 plus 2 left parenthesis negative space ion right parenthesis over denominator 2 end fraction space equals space 2 equals space sp
Hence comma space in space the space cabanion comma space CH subscript 3 straight C identical to straight C to the power of minus comma space
pair space of space electron space as space left parenthesis negative ve right parenthesis space charge space is space present space in space sp space minus hybridised space orbital.
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7.

Equal moles of hydrogen and oxygen gases are placed in a container with a pin-hole through which both can escape. What fraction of the oxygen escapes in the time required for one-half of the hydrogen to escape?

  • 1/4

  • 3/8

  • 1/2

  • 1/2


D.

1/2

we have given, 
a number of moles of hydrogen andleft parenthesis straight n subscript straight H subscript 2 end subscript right parenthesis that of oxygen areleft parenthesis straight n subscript straight O subscript 2 end subscript right parenthesis not equal.
therefore space We space have comma space the space relation space between space ratio space of space number space of space moles space
escaped space and space ratio space of space molecular space mass.
straight n subscript straight O subscript 2 end subscript over straight n subscript straight H subscript 2 end subscript space equals space square root of straight M subscript straight H subscript 2 end subscript over straight M subscript straight O subscript 2 end subscript end root


where comma space straight M space equals space molecular space mass space of space the space molecules.
straight n subscript straight O subscript 2 end subscript over straight n subscript straight H subscript 2 end subscript space equals space square root of 2 over 32 end root
straight n subscript straight O subscript 2 end subscript over straight n subscript straight H subscript 2 end subscript space equals space square root of 1 over 16 end root

fraction numerator straight n subscript straight O subscript 2 end subscript over denominator 0.5 end fraction space equals space 1 fourth

straight n subscript straight O subscript 2 end subscript space equals fraction numerator 0.5 over denominator 4 end fraction space equals 1 divided by 8

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8.

Consider the molecules CH4, NH3 and H2O. Which of the given statement is false?

  • The H-O-H bond angle in H2O  is larger than the H-C-H bond angle in CH4.

  • The H-O-H bond angle in H2O is smaller than the H-N-H bond angle in NH3.

  • The H-C-H bond angle in CH4 is larger than the H-N-H bond angle in NH3

  • The H-C-H bond angle in CH4 is larger than the H-N-H bond angle in NH3


A.

The H-O-H bond angle in H2O  is larger than the H-C-H bond angle in CH4.

According to VBT: lone pair-lone pair repulsion is more than a bond pair -lone pair repulsion.
As the number of lone pair of electrons on central element increases, repulsion between that lone pair of electrons increases and therefore, bond angle decreases.

Molecules

Bond angle

CH4 (no lone pair of electrons)

1090.5

NH3(one lone pair of electrons)

107.50

H2O (two lone pair of electrons)

104.450

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9.

The correct thermodynamic conditions for  the spontaneous reaction at all temperatures is

  • ΔH> 0 and Δ S< 0
  • ΔH< 0 and ΔS > 0
  • ΔH ΔS >0
  • ΔH ΔS >0

B.

ΔH< 0 and ΔS > 0

According to the Gibbs-Helmholtz reaction for spontaneity as,

ΔG =ΔH-TΔS

For reaction to being spontaneous, ΔG must be negative.
For this ΔH should be negative ΔS should be positive.
therefore,

ΔHΔS >0.


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10.

The addition of a catalyst during a chemical reaction alters which of the following quantities ?

  • Internal energy

  • Enthalpy

  • Activation energy

  • Activation energy


C.

Activation energy

A catalyst is a substance which alters the reaction but itself remains unchanged in the chemical reaction. In a chemical reaction, it provides a new reaction path by the lowering the activation energy barrier.


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