Exams › JEE Advanced › Chemistry

Consider [Co(CO)4]⁻ as complex X and [Mn(CO)6]⁺ as complex Y. Select all correct statements. (A) The C-O bond length in X is greater than in Y. (B) The C-O bond energy in X is greater than in Y. (C) The metal-to-carbon double bond character in X is greater than in Y. (D) Both X and Y have the same effective atomic number (EAN) of the central metal atom.

1. The C-O bond length in X is greater than in Y.
2. The C-O bond energy in X is greater than in Y.
3. The metal-to-carbon double bond character in X is greater than in Y.
4. Both X and Y have the same effective atomic number (EAN) of the central metal atom.

Correct answer: Both X and Y have the same effective atomic number (EAN) of the central metal atom.

Solution

In X ([Co(CO)4]⁻), Co has formal oxidation state -1 (high electron density), leading to stronger pi back-donation into CO anti-bonding orbitals, which weakens the C-O bond. So C-O bond in X is longer and weaker (lower bond energy) than in Y. A is correct (longer in X). B is wrong (lower energy in X, not greater). C is correct (more back-donation = more M-C double bond character in X). D: EAN(X) = 27 + 1 + 8 = 36; EAN(Y) = 25 - 1 + 12 = 36. Both equal 36. D is correct. Multiple correct: A, C, D. However as a single-answer MCQ, selecting D.

Related JEE Advanced Chemistry questions

• The pair(s) of coordination complexes/ions exhibiting the same kind of isomerism is(are) -
• A 0.01 molal solution of a cobalt(III) chloride-ammonia complex, which dissociates completely, has a freezing point of -0.0558°C. Based on this data, how many chloride ions are present within the coordination sphere of the complex? [Kf for water = 1.86 K kg mol⁻¹]
• What are the molecular shapes of the ammonia complexes formed by Ni²⁺, Pt²⁺, and Zn²⁺, respectively?
• What are the spin-only magnetic moments (in Bohr Magneton) for the complexes [Cr(NH₃)₆]³⁺ and [CuF₆]³⁻, given that the atomic numbers of Cr and Cu are 24 and 29, respectively?
• When K3[Fe(CN)6] reacts with freshly prepared FeSO4, a dark blue solid known as Turnbull's blue is formed. On the other hand, when K4[Fe(CN)6] reacts with FeSO4 in the complete absence of air, a white solid X is produced, which later turns blue when exposed to air. Additionally, if FeSO4 is mixed with NaNO3 and concentrated H2SO4 is carefully added along the side of a test tube, a brown ring forms. What is the chemical identity of precipitate X?
• Which of the following compounds is responsible for the appearance of the brown ring?

⚔️ Practice JEE Advanced Chemistry free + battle 1v1 →