Which one of the following aqueous solutions will be neutral ?

Which one of the following aqueous solutions will be neutral ?

NH₄Cl
NaCl
KCN
NaHSO₄
This question was previously asked in
UPSC CISF-AC-EXE – 2020
An aqueous solution is neutral if the salt dissolved in water is formed from the reaction of a strong acid and a strong base.
A) NH₄Cl is formed from a weak base (NH₄OH) and a strong acid (HCl). The solution will be acidic due to the hydrolysis of NH₄⁺ ions.
B) NaCl is formed from a strong base (NaOH) and a strong acid (HCl). The solution will be neutral as neither Na⁺ nor Cl⁻ ions undergo significant hydrolysis.
C) KCN is formed from a strong base (KOH) and a weak acid (HCN). The solution will be basic due to the hydrolysis of CN⁻ ions.
D) NaHSO₄ is sodium bisulfate. It is formed from a strong base (NaOH) and sulfuric acid (H₂SO₄), which is a strong acid. However, HSO₄⁻ is the conjugate base of the strong acid H₂SO₄, but it is also an acid itself that can donate a proton (HSO₄⁻ ⇌ H⁺ + SO₄²⁻). This makes the solution acidic.
Therefore, only NaCl forms a neutral aqueous solution.
The neutrality of an aqueous salt solution depends on the strength of the parent acid and base from which the salt is derived. Salts of strong acid and strong base yield neutral solutions. Salts of strong acid and weak base yield acidic solutions. Salts of weak acid and strong base yield basic solutions. Salts of weak acid and weak base yield solutions whose pH depends on the relative strengths of the weak acid and weak base.
Hydrolysis is the reaction of an ion with water. Cations of weak bases undergo acidic hydrolysis, releasing H⁺ ions. Anions of weak acids undergo basic hydrolysis, releasing OH⁻ ions. Cations of strong bases and anions of strong acids do not undergo significant hydrolysis.