Question

Given below are two statements: One is labelled as "Assertion A" and the other is labelled as "Reason R".
Assertion A: In the complex Ni(CO), and Fe(CO)s, the metals have zero oxidation state.
Reason R: Low oxidation states are found when a complex has ligands capable of π-donor character in addition to the o-bonding.
In the light of the above statements, choose the most appropriate answer from the option given below.

• A. Both A and R are correct and R is the correct explanation of A.
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Answer 1

The Correct Option is C

The given question involves analyzing two statements: Assertion A and Reason R, and determining their correctness and relationship.

Assertion A: In the complex Ni(CO)₄ and Fe(CO)₅, the metals have zero oxidation state.

The assertion is correct. In coordination chemistry, when carbonyl (CO) ligands bond with metals, they donate a pair of electrons to the metal center without altering the metal's oxidation state. Therefore, metals like Ni and Fe in Ni(CO)₄ and Fe(CO)₅ are in a zero oxidation state.

Reason R: Low oxidation states are found when a complex has ligands capable of π-donor character in addition to the σ-bonding.

This reason is incorrect in the context of this question. CO is a stronger π-acceptor (π-acid) rather than a π-donor ligand. It has empty π* orbitals that allow back donation of electrons from the metal into these orbitals, which stabilizes low oxidation states, rather than the metal donating electrons directly to the ligand.

Let's analyze the options:

• Both A and R are correct and R is the correct explanation of A: Although both statements might appear plausible individually, R is not the correct explanation of A because R incorrectly describes the nature of CO ligands as π-donor rather than the correct π-acceptor behavior.
• Both A and R are correct but R is NOT the correct explanation of A: This is a possible option, but R is not correct in the context of CO ligands.
• A is correct but R is not correct: This is indeed correct because A correctly states the oxidation state of the metals in the complexes while R provides an incorrect rationale about ligand character affecting oxidation states.
• A is not correct but R is correct: This is incorrect as A is a correct statement.

Conclusion: The correct answer is A is correct but R is not correct. The assertion is correctly explained by the nature of CO ligands being strong π-acceptors that stabilize low oxidation states in metals without contributing to it as π-donors.