A salt solution which gives a reddish-brown precipitate with NaOH and a white precipitate with BaCl₂ solution is:

1. CuSO₄
2. Ca(NO₃)₂
3. Fe₂(SO₄)₃
4. FeCl₃

Fe₂(SO₄)₃

Reason —

Reddish-brown ppt with NaOH indicates Fe³⁺ ions.
$\text{Fe}^{3+} + 3\text{OH}^- \rightarrow \text{Fe(OH)}_3 \downarrow \space (\text{reddish-brown})$

White ppt with BaCl₂ indicates SO₄^2- ions (forms insoluble BaSO₄)
$\text{Ba}^{2+} + \text{SO}$4^{2-} \rightarrow \text{BaSO}4 \downarrow \space (\text{white})

So the salt must contain Fe³⁺ and SO₄^2-, which is Fe₂(SO₄)₃.