MHTCET 18 Apr 2026 Shift 1 Paper

Concept:Effective atomic number (EAN) is calculated using the metal's atomic number, its oxidation state, and electrons donated by ligands.Explanation:In $\mathrm{Fe}(\mathrm{CO})_5$, each $\mathrm{CO}$ ligand is neutral, so the oxidation state of Fe is $0$.The atomic number of Fe is $Z = 26$.Each $\mathrm{CO}$ ligand donates $2$ electrons. Thus, five $\mathrm{CO}$ ligands donate $5 \times 2 = 10$ electrons.Using the EAN formula: $\mathrm{EAN} = Z - \text{oxidation state} + \text{electrons donated by ligands}$.Substitute the values: $\mathrm{EAN} = 26 - 0 + 10 = 36$.Answer:The EAN of Fe in $\mathrm{Fe}(\mathrm{CO})_5$ is $36$, which is Option B.