MHTCET 15 Apr 2026 Shift 1 Paper

Concept:The net charge of a complex ion is the sum of the metal and ligand charges, while the coordination number is the total number of donor atoms attached to the metal.Explanation:The chloride ion $\mathrm{Cl}^-$ is outside the coordination sphere, so the complex ion is$$\left[\mathrm{M}(\mathrm{en})_2(\mathrm{C}_2\mathrm{O}_4)\right]^+$$Let the oxidation number of M be $x$.The ligand en (ethane-1,2-diamine) is neutral.The oxalate ligand $\mathrm{C}_2\mathrm{O}_4^{2-}$ has a charge of $-2$.Therefore, the charge balance is:$$x + 2(0) + (-2) = +1$$$$x - 2 = +1$$$$x = +3$$So, the oxidation number of M is $+3$.Now, to find the coordination number:Each en is a bidentate ligand, providing 2 donor atoms.Two en ligands contribute $2 \times 2 = 4$ donor atoms.The oxalate ligand is also bidentate, contributing 2 donor atoms.Hence, the coordination number is $4 + 2 = 6$.Thus, the sum is:$$\text{Coordination number} + \text{Oxidation number} = 6 + 3 = 9$$Answer:Option A, 9.