Which of the statements are correct?

Options

A. (a) `Be_2C+H_2Orarr` Marsh gas
B. (b) `Al_4C_3+H_2Orarr` Gas is a content of CNG
C. (c) `CaC_2+H_2Orarr` Gas is used for welding purpose with `O_2` gas
D. (d) `Ca_3P_2+H_2Orarr` Gas is used in Holme signals with `CaC_2`

Explanation

To determine which statements are correct regarding the reactions of various carbides with water, we can analyze each statement step by step.

### Step-by-Step Solution:

1. **Beryllium Carbide Reaction**:
- **Reaction**: \( \text{Be}_2\text{C} + 4\text{H}_2\text{O} \rightarrow 2\text{Be(OH)}_2 + \text{CH}_4 \)
- **Analysis**: The reaction produces methane (CH4), which is also known as marsh gas. Therefore, this statement is **correct**.

2. **Aluminium Carbide Reaction**:
- **Reaction**: \( \text{Al}_4\text{C}_3 + 12\text{H}_2\text{O} \rightarrow 4\text{Al(OH)}_3 + 3\text{CH}_4 \)
- **Analysis**: The reaction produces methane (CH4), which is a component of compressed natural gas (CNG). Thus, this statement is also **correct**.

3. **Calcium Carbide Reaction**:
- **Reaction**: \( \text{CaC}_2 + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C}_2\text{H}_2 \)
- **Analysis**: The reaction produces acetylene (C2H2), which is used in welding with oxygen (O2). Therefore, this statement is **correct**.

4. **Calcium Phosphide Reaction**:
- **Reaction**: \( \text{Ca}_3\text{P}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Ca(OH)}_2 + 2\text{PH}_3 \)
- **Analysis**: The reaction produces phosphine (PH3), which is not typically associated with welding or halogen signals. This statement is **incorrect**.

### Conclusion:
- The correct statements are:
- Statement 1 (Beryllium carbide produces marsh gas).
- Statement 2 (Aluminium carbide produces methane, a component of CNG).
- Statement 3 (Calcium carbide produces acetylene used in welding).
- Statement 4 is incorrect.

### Final Answer:
- Statements 1, 2, and 3 are correct. Statement 4 is incorrect.