Which of the following solutions have `pH lt 7`.

Options

A. `BaI_(2)`
B. `AI(NO_(3))_(3)`
C. `CH_(3)COONH_(4)`
D. `CsI`

Explanation

To determine which of the given solutions have a pH less than 7, we need to analyze the nature of each solution based on the acids and bases that form them.

### Step-by-Step Solution:

1. **Identify the Nature of Each Solution:**
- **BaI2 (Barium Iodide)**: This salt is formed from Barium hydroxide (a strong base) and Hydroiodic acid (a strong acid). The pH of this solution will be neutral (pH = 7).

- **Al(NO3)3 (Aluminum Nitrate)**: This salt is formed from Aluminum hydroxide (a weak base) and Nitric acid (a strong acid). Since it is a salt of a weak base and a strong acid, it will have a pH less than 7.

- **CH3COONa (Sodium Acetate)**: This salt is formed from Acetic acid (a weak acid) and Sodium hydroxide (a strong base). The pH of this solution will be greater than 7 because it is a salt of a weak acid and a strong base.

- **NaCl (Sodium Chloride)**: This salt is formed from Hydrochloric acid (a strong acid) and Sodium hydroxide (a strong base). The pH of this solution will also be neutral (pH = 7).

2. **Conclusion:**
- Among the given options, only **Al(NO3)3** has a pH less than 7.

### Final Answer:
The solution that has a pH less than 7 is **Al(NO3)3**.

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