The basic oxide of chromium is:

The correct answer is Option (1) → \(CrO\)

For a transition metal, the lowest oxide is basic and the highest is acidic or amphoteric. As the oxidation state of the metal rises, its oxides become more covalent and more acidic.

The oxidation states of chromium in the given oxides:

• CrO: x + (−2) = 0, x = +2 — basic

• \( \ce{Cr2O3} \): 2x + 3(−2) = 0, x = +3 — amphoteric

• \( \ce{CrO2} \): x + 2(−2) = 0, x = +4

• \( \ce{CrO3} \): x + 3(−2) = 0, x = +6 — acidic (gives \( \ce{H2CrO4} \) and \( \ce{H2Cr2O7} \))

So the basic oxide of chromium is CrO.

NCERT (2026-27 edition):
Oxides and Oxoanions of Metals – “… As the oxidation number of a metal increases, ionic character decreases. In the case of Mn, Mn₂O₇ is a covalent green oil. Even CrO₃ and V₂O₅ have low melting points. In these higher oxides, the acidic character is predominant. … The well characterised CrO is basic but Cr₂O₃ is amphoteric.”