JEE Chemistry 2025 Question with Solution

Given: A matching question on primary valency and secondary valency of coordination compounds.

Find: The correct matching between List-I and List-II.

Primary valency is the oxidation state of the central metal atom, while secondary valency is the coordination number.

For (A) $[Co(en)_2Cl_2]Cl$:

Two $en$ ligands are bidentate, so they contribute $4$ coordination sites, and two coordinated $Cl^-$ contribute $2$ more.

So, (A) - (I).

For (B) $[Pt(NH_3)_2Cl(NO_2)]$:

The ligands $NH_3, NH_3, Cl^-,$ and $NO_2^-$ give coordination number $4$.

So, (B) - (IV).

For (C) $Hg[Co(SCN)_4]$:

There are four $SCN^-$ ligands bonded to cobalt.

So, (C) - (II).

For (D) $[Mg(EDTA)]^{2-}$:

According to the extracted solution, $EDTA$ gives coordination number $6$ here.

So, (D) - (III).

Therefore, the correct matching is (A)-(I), (B)-(IV), (C)-(II), (D)-(III). The correct option is B.

Given: Match complexes with their primary and secondary valencies.

Find: Which option gives the correct set of pairs.

1. (A) $[Co(en)_2Cl_2]Cl$

• Primary valency of Co is $3$.
• Secondary valency is $6$.
• Hence (A) - (I).

2. (B) $[Pt(NH_3)_2Cl(NO_2)]$

• Primary valency of Pt is $2$.
• Secondary valency is $4$.
• Hence (B) - (IV).

3. (C) $Hg[Co(SCN)_4]$

• Primary valency of Co is $2$.
• Secondary valency is $4$.
• Hence (C) - (II).

4. (D) $[Mg(EDTA)]^{2-}$

• Primary valency of Mg is $2$.
• Secondary valency is $6$.
• Hence (D) - (III).

Thus the final matching is (A)-(I), (B)-(IV), (C)-(II), (D)-(III), so the correct option is B.