When zinc nitrate crystals are strongly heated it gives:

Options

A. `ZnO` white residue and brown vapours of `NO_2`gas.
B. `ZnO` black residue and brown vapours of `NO_2`gas.
C. `ZnO` white residue and yellow vapours of `NO_2`gas.
D. `ZnO` black residue and yellow vapours of `NO_2`gas.

Answer

To solve the question regarding the decomposition of zinc nitrate crystals upon strong heating, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compound**: The compound in question is zinc nitrate, which has the chemical formula \( \text{Zn(NO}_3\text{)}_2 \).

2. **Understand the Decomposition Reaction**: When zinc nitrate is heated, it undergoes thermal decomposition. The general reaction for the decomposition of zinc nitrate can be represented as:
\[ 2 \text{Zn(NO}_3\text{)}_2 \rightarrow 2 \text{ZnO} + 4 \text{NO}_2 + \text{O}_2 \]
This indicates that zinc nitrate decomposes to form zinc oxide, nitrogen dioxide, and oxygen.

3. **Identify the Products**: From the balanced equation, we can see that the products of the reaction are:
- Zinc oxide (\( \text{ZnO} \)), which is a white solid residue.
- Nitrogen dioxide (\( \text{NO}_2 \)), which is a brown gas.
- Oxygen gas (\( \text{O}_2 \)), which is typically not colored.

4. **Conclusion**: Therefore, when zinc nitrate crystals are strongly heated, they yield a white residue of zinc oxide and brown vapors of nitrogen dioxide gas.

5. **Select the Correct Option**: Based on the products formed, the correct answer to the question is:
- Zinc oxide (white residue) and brown vapors of nitrogen dioxide gas.

### Final Answer:
When zinc nitrate crystals are strongly heated, it gives zinc oxide (white residue) and brown vapors of nitrogen dioxide gas.

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