`PbCl_(2)` is soluble in (a) ____. `AgCl` is soluble in (b) _____ white `Hg_(2)Cl_(2)` is (c ) ___by `NH_(3)`

Answer

To solve the question regarding the solubility of `PbCl2`, `AgCl`, and the reaction of `Hg2Cl2` with `NH3`, we will analyze each part step by step.

### Step-by-Step Solution

1. **Solubility of PbCl2**:
- Lead(II) chloride (`PbCl2`) is known to be sparingly soluble in cold water but becomes soluble in hot water. Therefore, the answer for the first blank is:
- **(a) hot water**

2. **Solubility of AgCl**:
- Silver chloride (`AgCl`) is insoluble in water but is soluble in aqueous ammonia (`NH3`). This is due to the formation of a soluble complex. Thus, the answer for the second blank is:
- **(b) aqueous NH3**

3. **Reaction of Hg2Cl2 with NH3**:
- Mercurous chloride (`Hg2Cl2`), when treated with ammonia, forms a black precipitate. This occurs due to the formation of a complex and the precipitation of mercury. Therefore, the answer for the third blank is:
- **(c) blackened by NH3**

### Final Answers:
- (a) hot water
- (b) aqueous NH3
- (c) blackened by NH3