Which of the following carbides reacts with `H_2O` to form propyne ?

Options

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

Answer

To solve the question of which carbide reacts with water (H₂O) to form propyne (C₃H₄), we will analyze the reactions of the given carbides with water step by step.

### Step 1: Identify the Carbides
The carbides we need to consider are:
1. Al₄C₃ (Aluminum carbide)
2. CaC₂ (Calcium carbide)
3. SiC (Silicon carbide)
4. Mg₂C₃ (Magnesium carbide)

### Step 2: React Al₄C₃ with H₂O
When aluminum carbide (Al₄C₃) reacts with water, the reaction can be represented as:
\[ \text{Al}_4\text{C}_3 + 12 \text{H}_2\text{O} \rightarrow 4 \text{Al(OH)}_3 + 3 \text{CH}_4 \]
- Products: Aluminum hydroxide (Al(OH)₃) and methane (CH₄).
- **Conclusion**: This does not produce propyne.

### Step 3: React CaC₂ with H₂O
Next, we react calcium carbide (CaC₂) with water:
\[ \text{CaC}_2 + 2 \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C}_2\text{H}_2 \]
- Products: Calcium hydroxide (Ca(OH)₂) and acetylene (C₂H₂).
- **Conclusion**: This does not produce propyne.

### Step 4: React SiC with H₂O
Now, we check silicon carbide (SiC):
\[ \text{SiC} + 2 \text{H}_2\text{O} \rightarrow \text{Si(OH)}_4 + \text{CH}_4 \]
- Products: Silicic acid (Si(OH)₄) and methane (CH₄).
- **Conclusion**: This does not produce propyne.

### Step 5: React Mg₂C₃ with H₂O
Finally, we react magnesium carbide (Mg₂C₃) with water:
\[ \text{Mg}_2\text{C}_3 + 6 \text{H}_2\text{O} \rightarrow 2 \text{Mg(OH)}_2 + \text{C}_3\text{H}_4 \]
- Products: Magnesium hydroxide (Mg(OH)₂) and propyne (C₃H₄).
- **Conclusion**: This produces propyne.

### Final Answer
Based on the reactions, the carbide that reacts with water to form propyne is **Mg₂C₃ (Magnesium carbide)**.