Qualitative tests identify Fe²⁺ and SO₄²⁻ ions Steps:

• Green precipitate with dilute NaOH, soluble in excess to green solution, points to Fe²⁺ forming Fe(OH)₂.
• No precipitate on adding dilute HNO₃ to the green solution confirms non-amphoteric behavior, ruling out Cr³⁺.
• White precipitate with aqueous Ba(NO₃)₂ indicates SO₄²⁻ forming insoluble BaSO₄.
• No precipitate with aqueous AgNO₃ confirms absence of halides like Cl⁻.

Why C is correct:

• Fe²⁺ produces dirty green Fe(OH)₂ precipitate with NaOH (often appearing as green suspension in excess); SO₄²⁻ forms white BaSO₄ with Ba²⁺ but no precipitate with Ag⁺, per solubility rules.

Why the others are wrong:

• A. Cr³⁺ forms green Cr(OH)₃ soluble in excess NaOH, but HNO₃ reprecipitates it; Cl⁻ forms white AgCl.
• B. Fe³⁺ forms brown Fe(OH)₃ insoluble in excess NaOH; Cl⁻ forms AgCl but no BaSO₄.
• D. Fe³⁺ forms brown Fe(OH)₃ insoluble in excess NaOH, not green.

Final answer: C