jee main chemistry important questions | Chemical Bonding And Molecular Structure

Q 1 :

Number of molecules/species from the following having one unpaired electron is __________.

$O_{2}, O_{2}^{- 1}, NO, {CN}^{- 1}, O_{2}^{2 -}$ [2024]

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Molecules	Number of electrons	Electronic configuration	Number of unpaired electrons
$O_{2}$	16	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{1}$	2
$O_{2}^{-}$	17	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{2} = π^{} 2 p_{y}^{1}$	1
$NO$	15	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{0}$	1
${CN}^{-}$	14	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < σ 2 p_{z}^{2}$	0
$O_{2}^{2 -}$	18	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{2} = π^{} 2 p_{y}^{2}$	0

Q 2 :

Number of molecules having bond order 2 from the following molecule is _________ .

$C_{2}, O_{2}, B e_{2}, L i_{2}, N e_{2}, N_{2}, H e_{2}$ [2024]

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Molecule	Electronic configuration	Bond order $= \frac{1}{2} [N_{b} - N_{a}]$
$C_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2}$	$\frac{1}{2} [8 - 4] = 2$
$O_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{1}$	$\frac{1}{2} [10 - 6] = 2$
${Be}_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2}$	$\frac{1}{2} [4 - 4] = 0$
${Li}_{2}$	$σ 1 s^{2} < σ^{*} 1 s^{2} < σ 2 s^{2}$	$\frac{1}{2} [4 - 2] = 1$
${Ne}_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{2} = π^{} 2 p_{y}^{2} < σ^{*} 2 p_{z}^{2}$	$\frac{1}{2} [10 - 10] = 0$
$N_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < σ 2 p_{z}^{2}$	$\frac{1}{2} [10 - 4] = 3$
${He}_{2}$	$σ 1 s^{2} < σ^{*} 1 s^{2}$	$\frac{1}{2} [2 - 2] = 0$

Q 3 :

The total number of species from the following in which one unpaired electron is present, in ____________ .

$N_{2}, O_{2}, C_{2}^{-}, O_{2}^{-}, O_{2}^{2 -}, H_{2}^{+}, {CN}^{-}, {He}_{2}^{+}$ [2024]

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Molecule	Electronic configuration	Number of unpaired electrons
$N_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < σ 2 p_{z}^{2}$	0
$O_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{1}$	2
$C_{2}^{-}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < σ 2 p_{z}^{1}$	1
$O_{2}^{-}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{2} = π^{} 2 p_{y}^{1}$	1
$O_{2}^{2 -}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{2} = π^{} 2 p_{y}^{2}$	0
$H_{2}^{+}$	$σ 1 s^{1}$	1
${CN}^{-}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < σ 2 p_{z}^{2}$	0
${He}_{2}^{+}$	$σ 1 s^{2} < σ^{*} 1 s^{1}$	1

Q 4 :

Total number of electrons present in $(π^{*})$ molecular orbitals of $O_{2}, O_{2}^{+}$ and $O_{2}^{-}$ is _________ . [2024]

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Molecule	Electronic configuration	*Electrons present in $π^{}$**
$O_{2}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{1}$	2
$O_{2}^{+}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{0}$	1
$O_{2}^{-}$	$σ 1 s^{2} < σ^{} 1 s^{2} < σ 2 s^{2} < σ^{} 2 s^{2} < σ 2 p_{z}^{2} < π 2 p_{x}^{2} = π 2 p_{y}^{2} < π^{} 2 p_{x}^{2} = π^{} 2 p_{y}^{1}$	3

Sum = 2 + 1 + 3 = 6

Q 5 :

When $ψ_{A}$ and $ψ_{B}$ are the wave function of atomic orbitals, then $σ^{*}$ is represented by: [2024]

$ψ_{A} - 2 ψ_{B}$
$ψ_{A} + ψ_{B}$
$ψ_{A} + 2 ψ_{B}$
$ψ_{A} - ψ_{B}$

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Constructive overlap of wavefunctions $(ψ_{A} + ψ_{B})$ give bonding molecular orbital ( $σ$ or $π$ ) and destructive overlap of wavefunctions $(ψ_{A} - ψ_{B})$ give antibonding molecular orbitals ( $σ^{*}$ or $π^{*}$ ). Axial overlap of orbitals give $σ$ (or $σ^{*}$ ) bond and lateral overlap of orbitals give $π$ (or $π^{*}$ ) bond.

Q 6 :

Which of the following linear combination of atomic orbitals will lead to formation of molecular orbitals in homonuclear diatomic molecules [internuclear axis in z-direction]?

(A)   $2 p_{z}$ and $2 p_{x}$

(B)   $2 s$ and $2 p_{x}$

(C)   $3 d_{x y}$ and $3 d_{x^{2} - y^{2}}$

(D)   $2 s$ and $2 p_{z}$

(E)   $2 p_{z}$ and $3 d_{x^{2} - y^{2}}$

Choose the correct answer from the options given below:   [2025]

(A) and (B) only
(E) only
(D) only
(C) and (D) only

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Q 7 :

Which of the following molecules(s) show/s paramagnetic behavior? [2025]

(A)   $O_{2}$
(B)   $N_{2}$
(C)   $F_{2}$
(D)   $S_{2}$
(E)   ${Cl}_{2}$

Choose the correct answer from the options given below:

B only
A and C only
A and E only
A and D only

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Molecule	Electronic Configuration	Number of Unpaired Electrons	Magnetic Nature
$O_{2}$	$σ 1 s^{2}, σ^{} 1 s^{2}, σ 2 s^{2}, σ^{} 2 s^{2}, σ 2 p_{z}^{2}, π 2 p_{x}^{2}, π 2 p_{y}^{2}, π^{} 2 p_{x}^{1}, π^{} 2 p_{y}^{1}$	2	Paramagnetic
$N_{2}$	$σ 1 s^{2}, σ^{} 1 s^{2}, σ 2 s^{2}, σ^{} 2 s^{2}, π 2 p_{x}^{2}, π 2 p_{y}^{2}, σ 2 p_{z}^{2}$	0	Diamagnetic
$F_{2}$	$σ 1 s^{2}, σ^{} 1 s^{2}, σ 2 s^{2}, σ^{} 2 s^{2}, σ 2 p_{z}^{2}, π 2 p_{x}^{2}, π 2 p_{y}^{2}, π^{} 2 p_{x}^{2}, π^{} 2 p_{y}^{2}$	0	Diamagnetic
$S_{2}$	$KK, LL, σ 3 s^{2}, σ^{} 3 s^{2}, σ 3 p_{z}^{2}, π 3 p_{x}^{2}, π 3 p_{y}^{2}, π^{} 3 p_{x}^{1}, π^{*} 3 p_{y}^{1}$	2	Paramagnetic
${Cl}_{2}$	$KK, LL, σ 3 s^{2}, σ^{} 3 s^{2}, σ 3 p_{z}^{2}, π 3 p_{x}^{2}, π 3 p_{y}^{2}, π^{} 3 p_{x}^{2}, π^{*} 3 p_{y}^{2}$	0	Diamagnetic

Q 8 :

What is the number of unpaired electron(s) in the highest occupied molecular orbital of the following species:

$N_{2};$ $N_{2}^{+};$ $O_{2};$ $O_{2}^{+}$ ? [2023]

0, 1, 2, 1
2, 1, 2, 1
0, 1, 0, 1
2, 1, 0, 1

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Species	Number of Unpaired Electrons
$(N_{2}) :$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) {(σ 2 p_{z})}^{2}$	0
$(N_{2}^{+}) :$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) {(σ 2 p_{z})}^{1}$	1
${(O}_{2}):$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} {(σ 2 p_{z})}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) (π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{1})$	2
${(O}_{2}^{+}):$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} {(σ 2 p_{z})}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) (π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{0})$	1

Q 9 :

According to MO theory the bond orders for $O_{2}^{2 -}$ , CO and ${NO}^{+}$ respectively, are [2023]

1, 3 and 3
2, 3 and 3
1, 2 and 3
1, 3 and 2

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Species	Molecular Orbital configuration	Bond order = $\frac{1}{2} (N_{b} - N_{a})$
$CO$	$KK$ ${}^{}σ_{2 s}^{2} σ_{2 s}^{ 2} (π_{2 p_{x}}^{2} \equiv π_{2 p_{y}}^{2}) σ_{2 p_{z}}^{2}$	$\frac{1}{2} (10 - 4) = 3$
${NO}^{+}$	$KK$ ${}^{}σ_{2 s}^{2} σ_{2 s}^{ 2} σ_{2 p_{z}}^{2} (π_{2 p_{x}}^{2} \equiv π_{2 p_{y}}^{2}) (π_{2 p_{x}^{0}}^{} \equiv π_{2 p_{y}^{0}}^{})$	$\frac{1}{2} (10 - 4) = 3$
$O_{2}^{- 2}$	$KK$ ${}^{}σ_{2 s}^{2} σ_{2 s}^{ 2} σ_{2 p_{z}}^{2} (π_{2 p_{x}}^{2} \equiv π_{2 p_{y}}^{2}) (π_{2 p_{x}}^{* 2} \equiv π_{2 p_{y}}^{* 2})$	$\frac{1}{2} (10 - 8) = 1$

Q 10 :

The bond order and magnetic property of acetylide ion are same as that of [2023]

$N_{2}^{+}$
${NO}^{+}$
$O_{2}^{+}$
$O_{2}^{-}$

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Species	Total number of electrons	Bond order	Unpaired electrons (n)	Magnetic momentum $\sqrt{(n \times (n + 2) BM)}$
Acetylides ion $(C_{2}^{- 2})$	14	3	0	0
$O_{2}^{-}$	17	1.5	1	$\sqrt{3}$
$O_{2}^{+}$	15	2.5	1	$\sqrt{3}$
$N_{2}^{+}$	13	2.5	1	$\sqrt{3}$
${NO}^{+}$	14	3	0	0

Species	Number of Unpaired Electrons
$(N_{2}) :$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) {(σ 2 p_{z})}^{2}$	0
$(N_{2}^{+}) :$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) {(σ 2 p_{z})}^{1}$	1
${(O}_{2}):$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} {(σ 2 p_{z})}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) (π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{1})$	2
${(O}_{2}^{+}):$ ${(σ 1 s)}^{2} {(σ^{} 1 s)}^{2} {(σ 2 s)}^{2} {(σ^{} 2 s)}^{2} {(σ 2 p_{z})}^{2} (π 2 p_{x}^{2} = π 2 p_{y}^{2}) (π^{} 2 p_{x}^{1} = π^{} 2 p_{y}^{0})$	1

Topic Question Set

Q 1 :

Number of molecules/species from the following having one unpaired electron is __________.

$O_{2}, O_{2}^{- 1}, NO, {CN}^{- 1}, O_{2}^{2 -}$ [2024]

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Q 2 :

Number of molecules having bond order 2 from the following molecule is _________ .

$C_{2}, O_{2}, B e_{2}, L i_{2}, N e_{2}, N_{2}, H e_{2}$ [2024]

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Q 3 :

The total number of species from the following in which one unpaired electron is present, in ____________ .

$N_{2}, O_{2}, C_{2}^{-}, O_{2}^{-}, O_{2}^{2 -}, H_{2}^{+}, {CN}^{-}, {He}_{2}^{+}$ [2024]

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Q 4 :

Total number of electrons present in $(π^{*})$ molecular orbitals of $O_{2}, O_{2}^{+}$ and $O_{2}^{-}$ is _________ . [2024]

0%

Q 5 :

When $ψ_{A}$ and $ψ_{B}$ are the wave function of atomic orbitals, then $σ^{*}$ is represented by: [2024]

Q 7 :

Which of the following molecules(s) show/s paramagnetic behavior? [2025]

(A)   $O_{2}$
(B)   $N_{2}$
(C)   $F_{2}$
(D)   $S_{2}$
(E)   ${Cl}_{2}$

Choose the correct answer from the options given below:

Q 8 :

What is the number of unpaired electron(s) in the highest occupied molecular orbital of the following species:

$N_{2};$ $N_{2}^{+};$ $O_{2};$ $O_{2}^{+}$ ? [2023]

Q 9 :

According to MO theory the bond orders for $O_{2}^{2 -}$ , CO and ${NO}^{+}$ respectively, are [2023]

Q 10 :

The bond order and magnetic property of acetylide ion are same as that of [2023]

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