NEET PYQ Bank: Chemical Bonding and Molecular Structure

Q 1 :
Given below are two statements: [2025]

Statement I: A hypothetical diatomic molecule with bond order zero is quite stable.
Statement II: As bond order increases, the bond length increases.

In the light of the above statements, choose the most appropriate answer from the options given below:

Statement I is true but statement II is false.
Statement I is false but statement II is true.
Both statement I and statement II are true.
Both statement I and statement II are false.

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(4)

Diatomic molecule with bond order zero does not exist. With increase in bond order, bond length decreases. Thus both statement-I and statement-II are false.

Q 2 :
Which one of the following statements is incorrect related to Molecular Orbital Theory? [2023]

The $π *$ anti-bonding molecular orbital has a node between the nuclei.
In the formation of bonding molecular orbital, the two electron waves of the bonding atoms reinforce each other.
Molecular orbitals obtained from $2 p_{x}$ and $2 p_{y}$ orbitals are symmetrical around the bond axis.
A $π$ -bonding molecular orbital has larger electron density above and below the internuclear axis.

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(3)

Molecular orbitals obtained from $2 p_{x}$ and $2 p_{y}$ orbitals are not symmetrical around the bond axis.

Q 3 :
The correct order of energies of molecular orbitals of $N_{2}$ molecules is [2023]

$σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < σ 2 p_{z} < σ^{*} 2 p_{z} < (π 2 p_{x} = π 2 p_{y}) < (π^{*} 2 p_{x} = π^{*} 2 p_{y})$
$σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < (π 2 p_{x} = π 2 p_{y}) < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ 2 p_{z} < σ^{*} 2 p_{z}$
$σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < (π 2 p_{x} = π 2 p_{y}) < σ 2 p_{z} < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ^{*} 2 p_{z}$
$σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < σ 2 p_{z} < (π 2 p_{x} = π 2 p_{y}) < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ^{*} 2 p_{z}$

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(3)

For molecules ${Li}_{2}, {Be}_{2}, B_{2}, C_{2}$ and $N_{2}$ , the order of energies of various molecular orbitals is

$σ 1 s < σ^{*} 1 s < σ 2 s < σ^{*} 2 s < (π 2 p_{x} = π 2 p_{y}) < σ 2 p_{z} < (π^{*} 2 p_{x} = π^{*} 2 p_{y}) < σ^{*} 2 p_{z}$

Q 4 :
Consider the following species: ${CN}^{+}, {CN}^{-}$ , NO and CN. Which one of these will have the highest bond order? [2018]

NO
${CN}^{-}$
${CN}^{+}$
CN

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(2)

$N O (15) :$ ${(σ 1 s)}^{2}, {(σ^{*} 1 s)}^{2}, {(σ 2 s)}^{2}, {(σ^{*} 2 s)}^{2}, {(σ 2 p_{z})}^{2}, {(π 2 p_{x})}^{2} = {(π 2 p_{y})}^{2}, {(π^{*} 2 p_{x})}^{1} = {(π^{*} 2 p_{y})}^{0}$

$B.O. = \frac{10 - 5}{2} = 2.5$

${CN}^{-} (14) :$ ${(σ 1 s)}^{2}, {(σ^{*} 1 s)}^{2}, {(σ 2 s)}^{2}, {(σ^{*} 2 s)}^{2}, {(π 2 p_{x})}^{2} = {(π 2 p_{y})}^{2}, {(σ 2 p_{z})}^{2}$

$B.O. = \frac{10 - 4}{2} = 3$

$CN (13) :$ ${(σ 1 s)}^{2}, {(σ^{*} 1 s)}^{2}, {(σ 2 s)}^{2}, {(σ^{*} 2 s)}^{2}, {(π 2 p_{x})}^{2} = {(π 2 p_{y})}^{2}, {(σ 2 p_{z})}^{1}$

$B.O. = \frac{9 - 4}{2} = 2.5$

${CN}^{+} (12) :$ ${(σ 1 s)}^{2}, {(σ^{*} 1 s)}^{2}, {(σ 2 s)}^{2}, {(σ^{*} 2 s)}^{2}, {(π 2 p_{x})}^{2} = {(π 2 p_{y})}^{2}$

$B.O. = \frac{8 - 4}{2} = 2$

Hence, $C N^{-}$ has highest bond order.

Q 5 :
Which one of the following pairs of species have the same bond order? [2017]

$O_{2}, {NO}^{+}$
${CN}^{-}, CO$
$N_{2}, O_{2}^{-}$
$CO, NO$

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(2)

Molecular orbital electronic configurations and bond order values are:

$O_{2} (16) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, σ 2 p_{z}^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}, π^{*} 2 p_{x}^{1} = π^{*} 2 p_{y}^{1}$

$B . O . = \frac{1}{2} (N_{b} - N_{a}) = \frac{1}{2} (10 - 6) = 2$

$N O^{+} (14) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, σ 2 p_{z}^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}$

$B . O . = \frac{1}{2} (10 - 4) = 3$

$C N^{-} (14) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}, σ 2 p_{z}^{2}$

$B . O . = \frac{1}{2} (10 - 4) = 3$

$C O (14) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}, σ 2 p_{z}^{2}$

$B . O . = \frac{1}{2} (10 - 4) = 3$

$N_{2} (14) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}, σ 2 p_{z}^{2}$

$B . O . = \frac{1}{2} (10 - 4) = 3$

$O_{2}^{-} (17) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, σ 2 p_{z}^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}, π^{*} 2 p_{x}^{2} = π^{*} 2 p_{y}^{1}$

$B . O . = \frac{1}{2} (10 - 7) = 1.5$

$N O (15) : σ 1 s^{2}, σ^{*} 1 s^{2}, σ 2 s^{2}, σ^{*} 2 s^{2}, σ 2 p_{z}^{2}, π 2 p_{x}^{2} = π 2 p_{y}^{2}, π^{*} 2 p_{x}^{1}$

$B . O . = \frac{1}{2} (10 - 5) = 2.5$

Topic Question Set

Q 1 :
Given below are two statements: [2025]

Statement I: A hypothetical diatomic molecule with bond order zero is quite stable.
Statement II: As bond order increases, the bond length increases.

In the light of the above statements, choose the most appropriate answer from the options given below:

Q 2 :
Which one of the following statements is incorrect related to Molecular Orbital Theory? [2023]

Q 3 :
The correct order of energies of molecular orbitals of $N_{2}$ molecules is [2023]

Q 4 :
Consider the following species: ${CN}^{+}, {CN}^{-}$ , NO and CN. Which one of these will have the highest bond order? [2018]

Q 5 :
Which one of the following pairs of species have the same bond order? [2017]

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Topic Question Set

Q 1 : Given below are two statements: [2025] Statement I: A hypothetical diatomic molecule with bond order zero is quite stable. Statement II: As bond order increases, the bond length increases. In the light of the above statements, choose the most appropriate answer from the options given below:

Q 2 : Which one of the following statements is incorrect related to Molecular Orbital Theory? [2023]

Q 3 : The correct order of energies of molecular orbitals of N2 molecules is [2023]

Q 4 : Consider the following species: CN+,CN-, NO and CN. Which one of these will have the highest bond order? [2018]

Q 5 : Which one of the following pairs of species have the same bond order? [2017]

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Q 1 :
Given below are two statements: [2025]

Statement I: A hypothetical diatomic molecule with bond order zero is quite stable.
Statement II: As bond order increases, the bond length increases.

In the light of the above statements, choose the most appropriate answer from the options given below:

Q 2 :
Which one of the following statements is incorrect related to Molecular Orbital Theory? [2023]

Q 3 :
The correct order of energies of molecular orbitals of $N_{2}$ molecules is [2023]

Q 4 :
Consider the following species: ${CN}^{+}, {CN}^{-}$ , NO and CN. Which one of these will have the highest bond order? [2018]

Q 5 :
Which one of the following pairs of species have the same bond order? [2017]