Ravi was asked to identify the cation present in the salt solution. He added one of the reagents given below and got a reddish-brown precipitate. The reagent that he used is:

1. Silver nitrate solution
2. Barium chloride solution
3. Ammonium hydroxide
4. Calcium chloride solution

Ammonium hydroxide

Reason — When iron (III) salts, having Fe³⁺ ions, are treated with ammonium hydroxide they give reddish brown precipitate, which is not soluble in excess ammonium hydroxide.

$\underset{\text{yellow solution}}{{\text{FeCl}$3}} + 3\text{NH}4\text{OH} \longrightarrow \underset{\text{reddish brown ppt}}{\text{Fe(OH)}3↓} + \underset{\text{colourless in solution}}{3\text{NH}4\text{Cl}}

$\underset{\text{Yellow solution}}{{\text{Fe}$2}(\text{SO}4)3} + 2\text{NH}4\text{OH} \longrightarrow \underset{\text{reddish brown ppt}}{2\text{Fe(OH)}3↓} + \underset{\text{colourless in solution}}{(3\text{NH}4)2\text{SO}4}