JEE Chemistry 2025 Question with Solution

Given: Pairs of transition metal ions are given.

Find: The pair having the same number of unpaired electrons.

The number of unpaired electrons depends on the electronic configuration of the ions.

For $\mathrm{V}^{2+}$:

It has $3$ unpaired electrons.

For $\mathrm{Co}^{2+}$:

It has $3$ unpaired electrons.

For $\mathrm{Ti}^{2+}$:

It has $2$ unpaired electrons.

For $\mathrm{Fe}^{3+}$:

It has $5$ unpaired electrons.

For $\mathrm{Cr}^{2+}$:

It has $4$ unpaired electrons.

For $\mathrm{Ti}^{3+}$:

It has $1$ unpaired electron.

For $\mathrm{Mn}^{2+}$:

It has $5$ unpaired electrons.

Thus, $\mathrm{V}^{2+}$ and $\mathrm{Co}^{2+}$ have the same number of unpaired electrons.

Therefore, the correct option is A.

Given: Four pairs of ions are listed.

Find: Which pair has equal numbers of unpaired electrons.

Remove electrons first from $4s$ and then count the $d$ electrons:

• $\mathrm{V}^{2+} : 3d^3$ gives $3$ unpaired electrons
• $\mathrm{Co}^{2+} : 3d^7$ also gives $3$ unpaired electrons

The first pair already matches, so no further comparison is needed to identify the correct choice.

Therefore, the correct option is A.