The pH is less than 7 for the solution of:A. FeC{l_3}B. NaCNC. NaOHD. NaCl

The correct answer is C. NaOH.

Sodium hydroxide (NaOH) is a strong base, and when dissolved in water, it completely dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻). Since hydroxide ions are basic, they increase the concentration of OH⁻ ions in solution, leading to a pH greater than 7. Therefore, the pH of a solution of NaOH is greater than 7.

The other options are:

A. FeCl₃ (Iron (III) chloride): This compound is a salt of a strong acid (HCl) and a weak base (Fe(OH)₃). The presence of the chloride ions does not significantly affect the pH of the solution. Iron (III) chloride hydrolyzes slightly in water, forming some acidic solution due to the hydrolysis of Fe³⁺ ions.

B. NaCN (Sodium cyanide): Cyanide ions (CN⁻) are a weak base, but since sodium cyanide dissociates completely in water, the solution will be basic due to the presence of hydroxide ions from the water and the weakly basic cyanide ions.

D. NaCl (Sodium chloride): Sodium chloride is a salt of a strong acid (HCl) and a strong base (NaOH). When dissolved in water, it dissociates into sodium ions (Na⁺) and chloride ions (Cl⁻). Since neither sodium nor chloride ions affect the pH of the solution, the pH of a solution of NaCl is neutral, around 7.