Ph Value

To solve the problem, we need to determine the pH value of an aqueous NaCl (sodium chloride) solution.

1. Understanding the pH of NaCl Solution:
Sodium chloride (NaCl) is a neutral salt formed from a strong acid (HCl) and a strong base (NaOH). When NaCl dissolves in water, it dissociates into Na⁺ and Cl⁻ ions, neither of which hydrolyze (react with water to form an acidic or basic solution).

2. pH of Neutral Solutions:
Since NaCl is a neutral salt, its aqueous solution does not affect the concentration of H⁺ or OH⁻ ions in water. Therefore, the pH of a NaCl solution is approximately 7, which is considered neutral.

Final Answer:
The pH value of an aqueous NaCl solution is 7 (Option D).

To solve the problem, we need to identify which solution has a pH less than 7.

1. Understanding pH Values:
- A solution with a pH less than 7 is acidic.
- A solution with a pH greater than 7 is basic.
- A solution with a pH of 7 is neutral (like pure water).

2. Analyzing the Given Solutions:

- Sodium chloride solution: Sodium chloride (NaCl) in water dissociates into sodium (Na+) and chloride (Cl-) ions, which do not affect the pH significantly. This solution is neutral, so its pH is 7, not less than 7.
- Sodium hydroxide solution: Sodium hydroxide (NaOH) is a strong base and will have a pH greater than 7.
- Acetic acid solution: Acetic acid (CH₃COOH) is a weak acid and will have a pH less than 7.
- Slaked lime: Slaked lime (calcium hydroxide, Ca(OH)₂) is a strong base and will have a pH greater than 7.

Final Answer:
The solution with pH less than 7 is Acetic acid solution (Option C).