JEE Main 2025 · 7 April · evening · Single correct · +4 / −1
Match List - I with List - II .
Choose the correct answer from the options given below :
| List - I (Complex) | List - II (Primary valency and Secondary valency) |
|---|---|
| (A) [Co(en)₂Cl₂]Cl | (I) 3, 6 |
| (B) [Pt(NH₃)₂Cl(NO₂)] | (II) 3, 4 |
| (C) Hg [Co(SCN)₄] | (III) 2, 6 |
| (D) [Mg (EDTA)]²⁻ | (IV) 2, 4 |
- (a) (A)-(I), (B)-(III), (C)-(II), (D)-(IV)
- (b) (A)-(II), (B)-(III), (C)-(IV), (D)-(I)
- (c) (A)-(I), (B)-(IV), (C)-(II), (D)-(III)
- (d) (A)-(III), (B)-(I), (C)-(II), (D)-(IV)
Answer and solution
Answer (c) (A)-(I), (B)-(IV), (C)-(II), (D)-(III)
Solution
Chemistry ma’am · 3 steps
Primary valency is the metal's oxidation state; secondary valency is how many donor atoms touch it.
- Two valencies. In Werner's theory, the primary valency is the oxidation state of the metal. The secondary valency is the coordination number. Count the donor atoms for it, not the ligands: en gives 2 and EDTA gives 6.
Complex Oxidation state (primary) Donor atoms (secondary) Match (A) [Co(en)₂Cl₂]Cl x - 2 - 1 = 0, so Co is +3 2 × 2 + 2 = 6 (I) 3, 6 (B) [Pt(NH₃)₂Cl(NO₂)] x - 1 - 1 = 0, so Pt is +2 2 + 1 + 1 = 4 (IV) 2, 4 (C) Hg[Co(SCN)₄] Hg is +2, so the anion is [Co(SCN)₄]²⁻ 4 (II), the slot left over (D) [Mg(EDTA)]²⁻ x - 4 = -2, so Mg is +2 6 (hexadentate) (III) 2, 6 - Fix the sure ones. A, B and D give unambiguous pairs, so they decide the answer. Only one option has A-(I), B-(IV) and D-(III). That leaves (II) for C, and its coordination number of 4 fits. Strictly, cobalt here is +2, not +3, so the 3 in (II) is a flaw in the list. It does not change the answer.
- So. The matching is (A)-(I), (B)-(IV), (C)-(II), (D)-(III), which is option (c).
The idea to keep. Find the oxidation state from the charges. Then count donor atoms, not ligands: en is 2, EDTA is 6. In matching questions, lock in the sure pairs first and let them pick the option.
Answer from the NTA final answer key. Solution by PrepWiser.