Tests confirm Fe³⁺ via green precipitate and NH₄⁺ via ammonia evolution

Steps:

• Aqueous NaOH added to J forms green Fe(OH)₃ precipitate, identifying Fe³⁺ ions.
• Heating the mixture yields no gas, showing Fe(OH)₃ stability without decomposition.
• Aluminium foil added to warmed alkaline mixture provides reducing conditions for NH₄⁺ to liberate NH₃ gas.
• NH₃ gas turns damp litmus blue, verifying NH₄⁺ presence alongside Fe³⁺.

Why D is correct:

• Fe³⁺ reacts with OH⁻ to form green Fe(OH)₃ precipitate (Fe³⁺ + 3OH⁻ → Fe(OH)₃ ↓); Al in alkaline medium aids NH₄⁺ liberation as NH₄⁺ + OH⁻ → NH₃ ↑ + H₂O.

Why the others are wrong:

• A: Fe²⁺ forms green Fe(OH)₂, but Al reduction yields no NH₃ specific to this sequence.
• B: Fe³⁺ present, but NO₃⁻ produces no green precipitate; Fe(OH)₃ is reddish-brown.
• C: Fe²⁺ gives green ppt, but NO₃⁻ reduction by Al fits better with brown ppt for Fe³⁺.

Final answer: D