Give the observation when each of the following is heated in a dry test tube. Also give balanced equations :
(a) `HgCO_(3) " " (b) NH_(4)NO_(2)`
(c ) `(NH_(4)Cl+NaNO_(3)) "mixture" " " (d) Pb(NO_(3))_(2)`

Explanation

To solve the problem, we will analyze each compound given in the question, describe the observations when they are heated in a dry test tube, and provide the balanced chemical equations for each reaction.

### (a) Heating of `HgCO3` (Mercury(II) Carbonate)

**Observation:**
When mercury(II) carbonate is heated, it decomposes to form mercury (Hg) and releases carbon dioxide (CO2) and oxygen (O2) gases.

**Balanced Equation:**
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