The hydrolysis of NH$_4$CI gives

Analyze the question

NH₄Cl is a salt. The question asks what kind of solution forms when it dissolves in water and undergoes hydrolysis.

Explain the concept

The nature of a salt solution depends on the acid and base that formed the salt:

• Strong acid + strong base gives a neutral solution (e.g., NaCl)
• Strong acid + weak base gives an acidic solution
• Weak acid + strong base gives an alkaline solution
• Weak acid + weak base depends on the relative strengths

Solution

NH₄Cl is formed from:

• HCl, a strong acid
• NH₃ (NH₄OH), a weak base

When dissolved in water, it dissociates completely:

NH₄Cl → NH₄⁺ + Cl⁻

• Cl⁻ is the conjugate base of a strong acid, so it does not react with water.
• NH₄⁺ is the conjugate acid of a weak base, so it hydrolyses:

NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺

This produces extra H₃O⁺ (H⁺) ions, so the solution has pH below 7 and is acidic.

Why not the others?

• B (alkaline): this would need excess OH⁻, which is not produced.
• C (buffer): a buffer needs a weak base and its conjugate acid in comparable amounts (e.g., NH₃ + NH₄Cl). Hydrolysis of NH₄Cl alone gives only a tiny amount of NH₃.
• D (neutral): this applies only to salts of strong acid + strong base.

Answer: A. an acidic solution

Exam tip: Remember "the stronger parent decides." HCl (strong) beats NH₃ (weak), so the solution is acidic. Similar salts that give acidic solutions: NH₄NO₃, (NH₄)₂SO₄, CuSO₄, and FeCl₃.