Verified Solution • 2025–26 Session moderate

QJEEM23Chd9fd: JEE Main 2023 Chemistry - Class 12 JEEM23Chd9fd Solution: Given below are two statements: one is labelled as "Assertion…

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)4 and Fe(CO)5, 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 σ\sigma -bonding.

In the light of the above statements, choose the most appropriate answer from the options given below

Multiple Choice Options

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

Step-by-Step Verified Solution

  • Option B: "A is correct but R is incorrect" is the right answer. Here is the reasoning:

    • Assertion A is correct. In the complex Ni(CO)4, if we assume the oxidation state of Ni to be x, we can set up the equation:

    x+(0×4)=0x + (0 \times 4) = 0

    From which we find that (x = 0).

    Similarly, in Fe(CO)5, if we let the oxidation state of Fe be y, the equation becomes:

    y+(0×5)=0y + (0 \times 5) = 0

    Solving this gives (y = 0).

    Therefore, the oxidation states of both Ni and Fe are zero in their respective complexes, verifying that Assertion A is true.

    Regarding Reason R, it is incorrect. The low oxidation states in these complexes are stabilized through synergic bonding, which involves the ligand being a π-acceptor, not a π-donor. The CO ligand in these complexes accepts electron density from the metal into its antibonding molecular orbitals, characterizing a π-acid ligand, and not a π-donor ligand as stated. Consequently, Reason R does not hold true.

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