Which is not obtained when metal carbides react with `H_(2)O`?

Options

A. `Al_(4)C_(3)+H_(2)O to CHequivCH`
B. `CaC_(2)+H_(2)O to CHequivCH`
C. `Mg_(4)C_(3)+H_(2)O to CH_(3)CequivCH`
D. `Be_(2)C+H_(2)O to CH_(4)`

Answer

To solve the question "Which is not obtained when metal carbides react with H₂O?", we can analyze the reactions of different metal carbides with water. Here’s a step-by-step solution:

### Step 1: Understand the Reaction of Metal Carbides with Water
Metal carbides generally react with water to produce a metal hydroxide and a hydrocarbon. The type of hydrocarbon produced can vary depending on the metal carbide involved.

### Step 2: Identify Common Metal Carbides
Some common metal carbides include:
- Aluminum carbide (Al₄C₃)
- Calcium carbide (CaC₂)
- Silicon carbide (SiC)

### Step 3: Analyze the Reaction of Each Carbide with Water
1. **Aluminum Carbide (Al₄C₃)**:
- Reaction: Al₄C₃ + 12 H₂O → 4 Al(OH)₃ + 3 CH₄ (methane)
- Products: Aluminum hydroxide and methane (an alkane).

2. **Calcium Carbide (CaC₂)**:
- Reaction: CaC₂ + 2 H₂O → Ca(OH)₂ + C₂H₂ (acetylene)
- Products: Calcium hydroxide and acetylene (an alkyne).

3. **Silicon Carbide (SiC)**:
- Reaction: SiC + 2 H₂O → SiO₂ + CH₄ (methane)
- Products: Silicon dioxide and methane (an alkane).

### Step 4: Identify the Incorrect Option
From the reactions analyzed:
- Aluminum carbide produces methane (alkane).
- Calcium carbide produces acetylene (alkyne).
- Silicon carbide produces methane (alkane).

The question asks which product is **not obtained**. Since aluminum carbide produces methane (not an alkyne), the statement in the question regarding the formation of an alkyne from aluminum carbide is incorrect.

### Conclusion
The correct answer to the question is that **an alkyne is not obtained when aluminum carbide reacts with water**.