KCET 2024 Chemistry Solved Paper

MnO is an ionic oxide in which manganese is present as $\text{Mn}^{2+}$ ($3d^5$) and oxygen as $\text{O}^{2-}$.In its rock-salt structure, each $\text{Mn}^{2+}$ ion is octahedrally surrounded by $\text{O}^{2-}$ ions, and adjacent $\text{Mn}^{2+}$ ions are bridged by $\text{O}^{2-}$.Through Mn–O–Mn superexchange, the spins on neighbouring $\text{Mn}^{2+}$ ions align in opposite directions.This produces two equal and opposite magnetic sublattices, so the net magnetic moment is zero.Therefore, MnO is antiferromagnetic below its Néel temperature ($T_N \approx 116\ \text{K}$) and becomes paramagnetic only above that temperature.Hence the correct option is Antiferromagnetisum.