JEE Main 2025 · 7 April · evening · Single correct · +4 / −1
'X' is the number of acidic oxides among VO₂, V₂O₃, CrO₃, V₂O₅ and Mn₂O₇. The primary valency of cobalt in
[Co(H₂NCH₂CH₂NH₂)₃]₂(SO₄)₃ is Y. The value of X + Y is _________.
- (a) 3
- (b) 4
- (c) 2
- (d) 5
Answer and solution
Answer (d) 5
Solution
Chemistry ma’am · 4 steps
Higher oxidation state means a more acidic oxide, and primary valency is the metal's oxidation state.
- Rule for oxides. For the same metal, the oxide gets more acidic as the oxidation state rises. Low states give basic oxides, middle states give amphoteric oxides, and high states such as +6 and +7 give acidic oxides.
Oxide Oxidation state of metal Nature V₂O₃ +3 basic VO₂ +4 amphoteric V₂O₅ +5 amphoteric (NCERT) CrO₃ +6 acidic Mn₂O₇ +7 acidic - Count X. Only CrO₃ and Mn₂O₇ are acidic, so X = 2.
- Find Y. Primary valency is the oxidation state of the metal. Ethylenediamine is neutral, and three SO₄²⁻ give -6, so each of the two complex ions carries +3. That makes Co +3, so Y = 3.
- So. X + Y = 2 + 3 = 5, which is option (d).
The idea to keep. Oxide nature follows oxidation state: low is basic, middle is amphoteric, high is acidic. In Werner's terms, primary valency is the oxidation state and secondary valency is the coordination number.
Answer from the NTA final answer key. Solution by PrepWiser.