Which of the following oxides is most basic?

The correct answer is Option (4) → MnO

For oxides of the same metal, the lower the oxidation state, the more basic the oxide. In a low oxidation state the metal ion is large and has a low charge, so the M–O bond is ionic and the oxide gives \( \ce{OH^{-}} \) with water/acid. In MnO manganese is in the +2 state, the lowest here, so MnO is the most basic.

Why the other options are incorrect

• Option (1) Mn₂O₇ — Incorrect. Mn is +7 (2x + 7(−2) = 0); this covalent oxide is strongly acidic (it gives permanganic acid \( \ce{HMnO4} \)).

• Option (2) Mn₂O₃ — Incorrect. Mn is +3 (2x + 3(−2) = 0); it is basic, but less basic than MnO.

• Option (3) MnO₂ — Incorrect. Mn is +4 (x + 2(−2) = 0); the oxide is amphoteric.

NCERT (2026-27 edition):
Oxides and Oxoanions of Metals – …