Find the number of metal oxides which are decomposed on normal heating from the gives oxides :
`Na_(2)O, Al_(2)O_(3), PbO, Ag_(2)O, HgO`.

Explanation

To solve the problem of finding the number of metal oxides that decompose on normal heating from the given oxides: \( \text{Na}_2\text{O}, \text{Al}_2\text{O}_3, \text{PbO}, \text{Ag}_2\text{O}, \text{HgO} \), we will analyze each oxide based on their thermal stability.

### Step-by-Step Solution:

1. **Identify the Oxides**: We have the following metal oxides:
- Sodium oxide (\( \text{Na}_2\text{O} \))
- Aluminum oxide (\( \text{Al}_2\text{O}_3 \))
- Lead oxide (\( \text{PbO} \))
- Silver oxide (\( \text{Ag}_2\text{O} \))
- Mercuric oxide (\( \text{HgO} \))

2. **Assess Thermal Stability**:
- **Sodium oxide (\( \text{Na}_2\text{O} \))**: Highly stable, does not decompose on heating.
- **Aluminum oxide (\( \text{Al}_2\text{O}_3 \))**: Highly stable, does not decompose on heating.
- **Lead oxide (\( \text{PbO} \))**: Generally stable, does not decompose on normal heating.
- **Silver oxide (\( \text{Ag}_2\text{O} \))**: Decomposes upon heating (around 200-300 °C) to yield silver and oxygen:
\[ 2 \text{Ag}_2\text{O} \rightarrow 4 \text{Ag} + \text{O}_2 \]
- **Mercuric oxide (\( \text{HgO} \))**: Decomposes upon heating (around 500-525 °C) to yield mercury and oxygen:
\[ 2 \text{HgO} \rightarrow 2 \text{Hg} + \text{O}_2 \]

3. **Count the Decomposable Oxides**: From the analysis above, only \( \text{Ag}_2\text{O} \) and \( \text{HgO} \) decompose on normal heating.

4. **Conclusion**: The total number of metal oxides that decompose on normal heating is 2.

### Final Answer:
The number of metal oxides that decompose on normal heating is **2**.

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