The reason to keep chloroform in dark brown coloured bottles is:

Options

A. To stop its oxidation
B. To stop its decomposition
C. To stop the formation of carbon tetrachloride from it
D. To stop its hydrolysis

Answer

### Step-by-Step Solution:

1. **Understanding Chloroform**: Chloroform (CHCl₃) is a chemical compound that can undergo various reactions when exposed to light and oxygen.

2. **Identifying the Problem**: The question asks why chloroform is stored in dark brown bottles. The options provided include:
- A) To stop its oxidation
- B) To stop its decomposition
- C) To stop the formation of carbon tetrachloride from it
- D) To stop its hydrolysis

3. **Analyzing the Options**:
- **Option A (To stop its oxidation)**: Chloroform can oxidize in the presence of light and oxygen, leading to the formation of phosgene gas (COCl₂), which is toxic.
- **Option B (To stop its decomposition)**: Decomposition is not the primary concern here; rather, oxidation is the issue.
- **Option C (To stop the formation of carbon tetrachloride)**: While carbon tetrachloride (CCl₄) can be formed from chloroform, this is not the main reason for using dark bottles.
- **Option D (To stop its hydrolysis)**: Hydrolysis is not a significant reaction for chloroform under normal conditions.

4. **Conclusion**: The primary reason for storing chloroform in dark brown bottles is to prevent its oxidation, which can lead to the formation of toxic phosgene gas. Therefore, the correct answer is **Option A: To stop its oxidation**.