A metallic carbide on treatment with water gives a colourless gas which burns readily in air and gives a precipitate with ammoniacal silver nitrate solution. The gas evolved is

Options

A. methane
B. ethane
C. acetylene
D. ethylene

Answer

To solve the question, we need to analyze the information given about the metallic carbide and the reactions that occur when it is treated with water.

### Step-by-Step Solution:

1. **Identify the Reaction**: The question states that a metallic carbide reacts with water to produce a colorless gas. A common example of a metallic carbide is calcium carbide (CaC₂).

2. **Write the Reaction**: When calcium carbide reacts with water, the reaction can be written as:
\[ \text{CaC}_2 + 2 \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{C}_2\text{H}_2 \]
Here, calcium hydroxide (Ca(OH)₂) and acetylene (C₂H₂) are produced. Acetylene is the colorless gas mentioned in the question.

3. **Properties of the Gas**: The problem states that the gas burns readily in air. Acetylene is known to burn with a bright flame, confirming that it meets this criterion.

4. **Reaction with Ammoniacal Silver Nitrate**: The question also mentions that the gas gives a precipitate with ammoniacal silver nitrate solution. When acetylene (C₂H₂) reacts with ammoniacal silver nitrate (Ag(NH₃)₂NO₃), it forms a white precipitate of disilver acetylide (Ag₂C₂):
\[ \text{C}_2\text{H}_2 + 2 \text{Ag(NH}_3\text{)}_2\text{NO}_3 \rightarrow \text{Ag}_2\text{C}_2 + 2 \text{NH}_4\text{NO}_3 \]
This confirms that acetylene reacts with ammoniacal silver nitrate to produce a white precipitate.

5. **Conclusion**: Based on the reactions and properties discussed, the colorless gas evolved from the reaction of the metallic carbide with water is acetylene (C₂H₂).

### Final Answer:
The gas evolved is acetylene (C₂H₂).

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