MHTCET 18 Apr 2026 Shift 2 Paper

Concept:The spectrochemical series arranges ligands in increasing order of their ability to cause crystal field splitting in the d-orbitals of the central metal ion.Explanation:Ligand field strength depends on the donor atom and the structure of the ligand.For the given ligands, the increasing order of field strength as per the spectrochemical series is:$$C_{2} \mathrm{O}_{4}^{2-} < \mathrm{H}_{2} \mathrm{O} < \mathrm{EDTA} < \mathrm{en}$$The oxalate ion $\left(\mathrm{C}_{2} \mathrm{O}_{4}^{2-}\right)$ is a weak field ligand because its donor oxygen atoms donate electron density less effectively.Water $\left(\mathrm{H}_{2} \mathrm{O}\right)$ is a stronger field ligand than oxalate.EDTA is even stronger because it is a hexadentate ligand with multiple donor atoms.Ethylenediamine (en), a bidentate ligand with nitrogen donor atoms, has the greatest field strength among the given ligands.Thus, the correct increasing order is:$$C_{2} \mathrm{O}_{4}^{2-} < \mathrm{H}_{2} \mathrm{O} < \mathrm{EDTA} < \mathrm{en}$$Answer:The correct option is C: $C_{2} \mathrm{O}_{4}^{2-} < \mathrm{H}_{2} \mathrm{O} < \mathrm{EDTA} < \mathrm{en}$.