Which of the following salt solutions has `pH lt7` ? .

Options

A. `NH_(4)F`
B. `Cr(NO_(3))_(3)`
C. `[(CN_(3))_(3)overset(o+)NH]CI^(Theta)`
D. `CaI_(2)`

Explanation

To determine which of the following salt solutions has a pH less than 7, we need to analyze the nature of each salt in relation to the acids and bases from which they are derived.

### Step-by-Step Solution:

1. **Identify the salts and their components:**
- **Option A: NH4F**
- This salt is formed from HF (hydrofluoric acid) and NH4OH (ammonium hydroxide).
- **Option B: Cr(NO3)3**
- This salt is formed from HNO3 (nitric acid) and Cr(OH)3 (chromium hydroxide).
- **Option C: [CN]3NH + Cl -**
- This salt is formed from HCl (hydrochloric acid) and CN^- (cyanide ion).
- **Option D: CaI2**
- This salt is formed from HI (hydroiodic acid) and Ca(OH)2 (calcium hydroxide).

2. **Determine the strength of acids and bases:**
- **NH4F:** HF is a weak acid and NH4OH is a weak base. The salt of a weak acid and weak base can have a pH less than 7.
- **Cr(NO3)3:** HNO3 is a strong acid and Cr(OH)3 is a weak base. The salt of a strong acid and weak base will have a pH less than 7.
- **[CN]3NH + Cl -:** HCl is a strong acid and CN^- is a weak base. The salt of a strong acid and weak base will have a pH less than 7.
- **CaI2:** HI is a strong acid and Ca(OH)2 is a strong base. The salt of a strong acid and strong base will have a pH equal to 7.

3. **Conclusion:**
- From the analysis:
- **NH4F** (weak base + strong acid) → pH < 7
- **Cr(NO3)3** (weak base + strong acid) → pH < 7
- **[CN]3NH + Cl -** (weak base + strong acid) → pH < 7
- **CaI2** (strong base + strong acid) → pH = 7

Thus, the salts that have a pH less than 7 are **NH4F, Cr(NO3)3, and [CN]3NH + Cl -**.

### Final Answer:
The salt solutions that have pH < 7 are **A (NH4F), B (Cr(NO3)3), and C ([CN]3NH + Cl -)**.