In which of the following processes, the bond order increases and paramagnetic character changes to diamagnetic one ?

Chemical Bonding and Molecular Structure PYQ — JEE Main 2023 · 13 Apr · Shift 1 · Q1 with Solution

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Correct answer: C

We need a process where:
- bond order increases, and
- paramagnetic changes to diamagnetic.
Recall molecular orbital facts:
- Bond order $= \dfrac{N_b - N_a}{2}$
- Paramagnetic: contains unpaired electron(s)
- Diamagnetic: all electrons paired

Option A: $\mathrm{O_2 \rightarrow O_2^{2-}}$

For $\mathrm{O_2}$

$\mathrm{O_2}$ has 16 electrons and MO configuration gives 2 unpaired electrons in $\pi^{*}_{2p}$ .

Bond order of $\mathrm{O_2} = 2$
It is paramagnetic

For $\mathrm{O_2^{2-}}$

Adding 2 electrons fills the antibonding $\pi^{*}_{2p}$ orbitals.

Bond order becomes $1$
It is diamagnetic

So, paramagnetic $\to$ diamagnetic is true, but bond order decreases from $2$ to $1$ .

❌ Not correct.

Option B: $\mathrm{N_2 \rightarrow N_2^+}$

For $\mathrm{N_2}$

Bond order $= 3$
All electrons paired, so diamagnetic

For $\mathrm{N_2^+}$

Removing one electron from bonding MO decreases bond order by $\tfrac{1}{2}$ .

Bond order $= 2.5$
One unpaired electron present, so paramagnetic

Here bond order decreases and diamagnetic $\to$ paramagnetic.

❌ Not correct.

Option C: $\mathrm{NO \rightarrow NO^+}$

For $\mathrm{NO}$

NO has 15 electrons.

It has one unpaired electron, so paramagnetic
Bond order of $\mathrm{NO} = 2.5$

For $\mathrm{NO^+}$

Removing one electron removes the unpaired electron from antibonding orbital.

Bond order increases to $3$
All electrons paired, so diamagnetic

Thus:

bond order increases: $2.5 \to 3$
paramagnetic $\to$ diamagnetic

✅ Correct.

Option D: $\mathrm{O_2 \rightarrow O_2^+}$

For $\mathrm{O_2}$

Bond order $= 2$
Paramagnetic

For $\mathrm{O_2^+}$

Removing one electron from antibonding orbital increases bond order to $2.5$ . But one unpaired electron still remains.

Bond order increases
Still paramagnetic

So paramagnetic does not change to diamagnetic.

❌ Not correct.

Final Answer

The only process in which bond order increases and paramagnetic character changes to diamagnetic is:

$\boxed{\mathrm{NO \rightarrow NO^+}}$

So the correct option is C.

Option A: $\mathrm{O_2 \rightarrow O_2^{2-}}$

For $\mathrm{O_2}$

$\mathrm{O_2}$ has 16 electrons and MO configuration gives 2 unpaired electrons in $\pi^{*}_{2p}$ .

Bond order of $\mathrm{O_2} = 2$
It is paramagnetic

For $\mathrm{O_2^{2-}}$

Adding 2 electrons fills the antibonding $\pi^{*}_{2p}$ orbitals.

Bond order becomes $1$
It is diamagnetic

So, paramagnetic $\to$ diamagnetic is true, but bond order decreases from $2$ to $1$ .

❌ Not correct.

Option B: $\mathrm{N_2 \rightarrow N_2^+}$

For $\mathrm{N_2}$

Bond order $= 3$
All electrons paired, so diamagnetic

For $\mathrm{N_2^+}$

Removing one electron from bonding MO decreases bond order by $\tfrac{1}{2}$ .

Bond order $= 2.5$
One unpaired electron present, so paramagnetic

Here bond order decreases and diamagnetic $\to$ paramagnetic.

❌ Not correct.

Option C: $\mathrm{NO \rightarrow NO^+}$

For $\mathrm{NO}$

NO has 15 electrons.

It has one unpaired electron, so paramagnetic
Bond order of $\mathrm{NO} = 2.5$

For $\mathrm{NO^+}$

Removing one electron removes the unpaired electron from antibonding orbital.

Bond order increases to $3$
All electrons paired, so diamagnetic

Thus:

bond order increases: $2.5 \to 3$
paramagnetic $\to$ diamagnetic

✅ Correct.

Option D: $\mathrm{O_2 \rightarrow O_2^+}$

For $\mathrm{O_2}$

Bond order $= 2$
Paramagnetic

For $\mathrm{O_2^+}$

Removing one electron from antibonding orbital increases bond order to $2.5$ . But one unpaired electron still remains.

Bond order increases
Still paramagnetic

So paramagnetic does not change to diamagnetic.

❌ Not correct.

Final Answer

The only process in which bond order increases and paramagnetic character changes to diamagnetic is:

$\boxed{\mathrm{NO \rightarrow NO^+}}$

So the correct option is C.

Chemical Bonding and Molecular Structure question

Chemical Bonding and Molecular Structure question

Option A: $\mathrm{O_2 \rightarrow O_2^{2-}}$

For $\mathrm{O_2}$

For $\mathrm{O_2^{2-}}$

Option B: $\mathrm{N_2 \rightarrow N_2^+}$

For $\mathrm{N_2}$

For $\mathrm{N_2^+}$

Option C: $\mathrm{NO \rightarrow NO^+}$

For $\mathrm{NO}$

For $\mathrm{NO^+}$

Option D: $\mathrm{O_2 \rightarrow O_2^+}$

For $\mathrm{O_2}$

For $\mathrm{O_2^+}$

Final Answer

More from Chemical Bonding and Molecular Structure

Chemical Bonding and Molecular Structure question

Chemical Bonding and Molecular Structure question

Option A: $\mathrm{O_2 \rightarrow O_2^{2-}}$

For $\mathrm{O_2}$

For $\mathrm{O_2^{2-}}$

Option B: $\mathrm{N_2 \rightarrow N_2^+}$

For $\mathrm{N_2}$

For $\mathrm{N_2^+}$

Option C: $\mathrm{NO \rightarrow NO^+}$

For $\mathrm{NO}$

For $\mathrm{NO^+}$

Option D: $\mathrm{O_2 \rightarrow O_2^+}$

For $\mathrm{O_2}$

For $\mathrm{O_2^+}$

Final Answer

More from Chemical Bonding and Molecular Structure

Option A: O2→O22−\mathrm{O_2 \rightarrow O_2^{2-}}O2​→O22−​

For O2\mathrm{O_2}O2​

For O22−\mathrm{O_2^{2-}}O22−​

Option B: N2→N2+\mathrm{N_2 \rightarrow N_2^+}N2​→N2+​

For N2\mathrm{N_2}N2​

For N2+\mathrm{N_2^+}N2+​

Option C: NO→NO+\mathrm{NO \rightarrow NO^+}NO→NO+

For NO\mathrm{NO}NO

For NO+\mathrm{NO^+}NO+

Option D: O2→O2+\mathrm{O_2 \rightarrow O_2^+}O2​→O2+​

For O2\mathrm{O_2}O2​

For O2+\mathrm{O_2^+}O2+​

Final Answer

More from Chemical Bonding and Molecular Structure

Option A: O2→O22−\mathrm{O_2 \rightarrow O_2^{2-}}O2​→O22−​

For O2\mathrm{O_2}O2​

For O22−\mathrm{O_2^{2-}}O22−​

Option B: N2→N2+\mathrm{N_2 \rightarrow N_2^+}N2​→N2+​

For N2\mathrm{N_2}N2​

For N2+\mathrm{N_2^+}N2+​

Option C: NO→NO+\mathrm{NO \rightarrow NO^+}NO→NO+

For NO\mathrm{NO}NO

For NO+\mathrm{NO^+}NO+

Option D: O2→O2+\mathrm{O_2 \rightarrow O_2^+}O2​→O2+​

For O2\mathrm{O_2}O2​

For O2+\mathrm{O_2^+}O2+​

Final Answer

More from Chemical Bonding and Molecular Structure

Option A: $\mathrm{O_2 \rightarrow O_2^{2-}}$

For $\mathrm{O_2}$

For $\mathrm{O_2^{2-}}$

Option B: $\mathrm{N_2 \rightarrow N_2^+}$

For $\mathrm{N_2}$

For $\mathrm{N_2^+}$

Option C: $\mathrm{NO \rightarrow NO^+}$

For $\mathrm{NO}$

For $\mathrm{NO^+}$

Option D: $\mathrm{O_2 \rightarrow O_2^+}$

For $\mathrm{O_2}$

For $\mathrm{O_2^+}$

Option A: $\mathrm{O_2 \rightarrow O_2^{2-}}$

For $\mathrm{O_2}$

For $\mathrm{O_2^{2-}}$

Option B: $\mathrm{N_2 \rightarrow N_2^+}$

For $\mathrm{N_2}$

For $\mathrm{N_2^+}$

Option C: $\mathrm{NO \rightarrow NO^+}$

For $\mathrm{NO}$

For $\mathrm{NO^+}$

Option D: $\mathrm{O_2 \rightarrow O_2^+}$

For $\mathrm{O_2}$

For $\mathrm{O_2^+}$