How many of the following reagents give pure white precipitate with an aqueous solution of Ag(I) salt ? Concentrated `HCl, Kl, K_2CrO_4, Na_2CO_3,NaCN` (in small amount), `K_4[Fe(CN)_6]`

Explanation

To determine how many of the given reagents produce a pure white precipitate with an aqueous solution of Ag(I) salt, we will analyze each reagent one by one.

1. **Concentrated HCl**:
- When Ag(I) reacts with HCl, it forms AgCl2^(-), which is soluble. Therefore, it does not produce a precipitate.
- **Result**: No precipitate.

2. **KI (Potassium Iodide)**:
- When Ag(I) reacts with I^(-) from KI, it forms AgI, which is a yellow precipitate.
- **Result**: No pure white precipitate.

3. **K2CrO4 (Potassium Chromate)**:
- When Ag(I) reacts with CrO4^(2-), it forms Ag2CrO4, which is red in color.
- **Result**: No pure white precipitate.

4. **Na2CO3 (Sodium Carbonate)**:
- When Ag(I) reacts with CO3^(2-), it forms Ag2CO3, which is yellowish-white in color.
- **Result**: No pure white precipitate.

5. **NaCN (Sodium Cyanide)**:
- When Ag(I) reacts with CN^(-), it forms AgCN, which is a white precipitate.
- **Result**: Produces a pure white precipitate.

6. **K4[Fe(CN)6] (Potassium Hexacyanoferrate(II))**:
- When Ag(I) reacts with [Fe(CN)6]^(4-), it forms Ag4[Fe(CN)6], which is also a white precipitate.
- **Result**: Produces a pure white precipitate.

### Summary of Results:
- Concentrated HCl: No precipitate
- KI: No pure white precipitate
- K2CrO4: No pure white precipitate
- Na2CO3: No pure white precipitate
- NaCN: Pure white precipitate
- K4[Fe(CN)6]: Pure white precipitate

### Final Count:
Only **2 reagents (NaCN and K4[Fe(CN)6])** produce a pure white precipitate with Ag(I) salt.