Identify the correct statement:

The correct answer is Option (3) → \(CrO\) is basic, \(Cr_2O_3\) is amphoteric, \(CrO_3\) is acidic

For the oxides of one transition metal, the acidic character increases with the oxidation state of the metal. In a high oxidation state the metal is small and highly charged, its bonds with oxygen are more covalent, and the oxide reacts with bases; in a low oxidation state the oxide is ionic and basic.

• CrO: Cr is +2 (lowest) ⇒ basic.

• Cr₂O₃: Cr is +3 (2x − 6 = 0) ⇒ amphoteric; it dissolves in both acids and alkalis.

• CrO₃: Cr is +6 (highest) ⇒ acidic; it gives \( \ce{H2CrO4} \) and \( \ce{H2Cr2O7} \) with water.

Shortcut: the oxide with the highest oxidation state must be acidic; only Options (3) and (4) say \( \ce{CrO3} \) is acidic, and of these only Option (3) has the low-state CrO basic.

Why the other options are incorrect

• Option (1) CrO acidic, Cr₂O₃ basic, CrO₃ amphoteric — Incorrect. It reverses the trend; the +2 oxide is the most basic.

• Option (2) CrO basic, Cr₂O₃ acidic, CrO₃ amphoteric — Incorrect. CrO is right, but the +6 oxide is more acidic than the +3 oxide, not less.

• Option (4) CrO amphoteric, Cr₂O₃ basic, CrO₃ acidic — Incorrect. \( \ce{CrO3} \) is right, but the amphoteric oxide is \( \ce{Cr2O3} \), and CrO is the basic one.

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. Thus, Mn₂O₇ gives HMnO₄ and CrO₃ gives H₂CrO₄ and H₂Cr₂O₇. … The well characterised CrO is basic but Cr₂O₃ is amphoteric.”