White precipitate of `AgCl` turns to greyish or black when:

Options

A. reacts with `Na_(3)AsO_(4)`
B. exposed to sunlight
C. reacts with `K_(2)CrO_(4)`
D. reacts with concentrated `HCl`

Answer

To solve the question of when the white precipitate of AgCl turns to greyish or black, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compound**: Recognize that AgCl is silver chloride, which is known to form a white precipitate.

2. **Understand the Reaction**: When AgCl is exposed to sunlight (or UV light), it undergoes a photochemical reaction. This reaction involves the decomposition of AgCl.

3. **Write the Decomposition Reaction**: The reaction can be expressed as:
\[ 2 \, \text{AgCl} \, \xrightarrow{\text{sunlight}} \, 2 \, \text{Ag} + \text{Cl}_2 \, (g) \]
Here, silver chloride decomposes into silver (Ag) and chlorine gas (Cl₂).

4. **Observe the Color Change**: The silver produced (Ag) appears as a greyish or blackish precipitate when formed, which is the result of the reduction of AgCl under sunlight.

5. **Conclusion**: Therefore, the white precipitate of AgCl turns greyish or black when it is exposed to sunlight.

### Final Answer:
The white precipitate of AgCl turns greyish or black when exposed to sunlight.

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