Which of the following carbides on treatment with water give methane ?

Options

A. ` CaC_2`
B. `Be_2C_`
C. `Al_4C_3`
D. `Mg_2C_3`

Explanation

To determine which of the given carbides produce methane when treated with water, we need to analyze the behavior of different carbides upon hydrolysis.

### Step-by-Step Solution:

1. **Understanding Carbides**:
- Carbides are compounds composed of carbon and a more electropositive element. They can be classified into different types based on their reactivity with water.

2. **Identifying Methanides**:
- Methanides are a specific type of carbide that, upon hydrolysis (reaction with water), produce methane (CH₄).

3. **Analyzing Aluminum Carbide (Al₄C₃)**:
- When aluminum carbide (Al₄C₃) reacts with water, it undergoes hydrolysis to produce methane:
\[ \text{Al}_4\text{C}_3 + 12\text{H}_2\text{O} \rightarrow 4\text{Al(OH)}_3 + 3\text{CH}_4 \]
- Therefore, Al₄C₃ is a methanide.

4. **Analyzing Calcium Carbide (CaC₂)**:
- Calcium carbide (CaC₂) reacts with water to produce acetylene (C₂H₂), not methane:
\[ \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C}_2\text{H}_2 \]
- Thus, CaC₂ is not a methanide.

5. **Analyzing Beryllium Carbide (Be₂C)**:
- Beryllium carbide (Be₂C) also reacts with water to produce methane:
\[ \text{Be}_2\text{C} + 4\text{H}_2\text{O} \rightarrow 2\text{Be(OH)}_2 + \text{CH}_4 \]
- Therefore, Be₂C is another example of a methanide.

6. **Analyzing Magnesium Carbide (Mg₂C₃)**:
- Magnesium carbide (Mg₂C₃) does not produce methane upon hydrolysis; it produces a different type of hydrocarbon:
\[ \text{Mg}_2\text{C}_3 + 6\text{H}_2\text{O} \rightarrow 2\text{Mg(OH)}_2 + 3\text{C}_2\text{H}_4 \]
- Hence, Mg₂C₃ is not a methanide.

### Conclusion:
The carbides that produce methane upon treatment with water are:
- **Aluminum carbide (Al₄C₃)**
- **Beryllium carbide (Be₂C)**