JEE Main · 2019 · 09 Apr 2019 · Shift 2 · Coordination Compounds

Valence bond theory pictures bonding through hybridised orbitals but says nothing about the splitting of the $d$ orbitals, so it cannot account for the colours of transition-metal complexes, which come from $d$-$d$ transitions, and statement I is correct. It also offers no basis for ranking ligands as weak-field or strong-field, since that ordering comes from crystal field theory, so statement III is correct. Statement II overreaches: valence bond theory can tell paramagnetic from diamagnetic by counting unpaired electrons but cannot predict magnetic moments quantitatively, so it is wrong. Statements I and III are the correct ones.