`NH_(4)Cl(s)` is heated in test tube.Vapours are brought in contract with red litmus paper, which changes to blue and then to red.It is because of :

Options

A. formation of `NH_(4)OH` and `HCl`
B. formation of `NH_(3)` and `HCl`
C. greater diffusion of `NH_(3)` than `HCl`
D. greater diffusion of `HCl` than `NH_(3)`

Explanation

To solve the problem, we need to analyze the reaction that occurs when ammonium chloride (NH₄Cl) is heated and how it interacts with red litmus paper.

### Step-by-Step Solution:

1. **Heating Ammonium Chloride**: When NH₄Cl is heated, it decomposes into ammonia (NH₃) and hydrogen chloride (HCl) gas. The reaction can be represented as:
\[ NH₄Cl(s) \rightarrow NH₃(g) + HCl(g) \]

2. **Contact with Red Litmus Paper**: The vapors produced (NH₃ and HCl) are then brought into contact with red litmus paper.

3. **Effect of HCl on Red Litmus**: HCl is an acidic gas. When it comes into contact with red litmus paper, it will cause the paper to change color from red to blue, indicating a basic reaction:
\[ HCl + \text{Red Litmus} \rightarrow \text{Blue Litmus} \]

4. **Effect of NH₃ on Litmus**: Ammonia is a basic gas. If ammonia diffuses and comes into contact with the litmus paper, it can also react with the red litmus paper, converting it back to red:
\[ NH₃ + \text{Blue Litmus} \rightarrow \text{Red Litmus} \]

5. **Diffusion Rates**: The key point here is the rate of diffusion of the gases. Ammonia (NH₃) diffuses faster than hydrogen chloride (HCl). This means that after HCl has turned the litmus paper blue, the ammonia will diffuse more quickly and react with the litmus paper, turning it back to red.

6. **Conclusion**: The final observation of the litmus paper changing from blue back to red is due to the greater diffusion of ammonia compared to hydrogen chloride. Therefore, the correct explanation for the observed change is that the greater diffusion of ammonia than HCl causes the litmus paper to revert to red after initially turning blue.

### Final Answer:
The correct answer is: **Greater diffusion of ammonia than HCl.**