`HCN+H_(2)Orarr[X]+NH_(3), [X]rarr[Y]+H_(2)O` (Unbalanced equations)
[Y] May be prepared by which one of the following methods?

Options

A. By dehydration of Malonic acid with `P_(2)O_(5)`
B. By thermal decomposition of carbon sub - oxide in air.
C. By heating potassium hexacyanoferrate (II) with conc. `H_(2)SO_(4)`
D. By the action of conc. `HNO_(3)` on charcoal.

Answer

To solve the problem, we need to analyze the given unbalanced chemical equations and determine the possible method for preparing compound Y.

### Step-by-Step Solution:

1. **Identify the Reactants and Products**:
- The first reaction is between HCN (hydrogen cyanide) and water (H₂O), producing an intermediate compound [X] and ammonia (NH₃).
- The second reaction involves [X] leading to [Y] with the elimination of water (H₂O).

2. **Determine the Structure of [X]**:
- When HCN reacts with water, it can form ammonium ion (NH₄⁺) and cyanide ion (CN⁻). The product [X] can be thought of as a compound that contains these ions. A likely candidate for [X] is ammonium cyanide (NH₄CN).

3. **Analyze the Formation of [Y]**:
- The transformation from [X] to [Y] involves heating [X] to remove water. This suggests that [Y] could be a compound formed by dehydration of [X].
- If we consider ammonium cyanide (NH₄CN), heating it could lead to the formation of cyanogen (C₂N₂) or other related compounds.

4. **Consider Possible Methods for Preparing [Y]**:
- The question asks which method can prepare [Y]. The options provided in the original question likely include:
- Dehydration of malonic acid with P₂O₅.
- Thermal decomposition of carbon suboxide (C₃O₂).
- Action of concentrated HNO₃ on charcoal.

5. **Evaluate Each Method**:
- **Dehydration of Malonic Acid with P₂O₅**: This method produces a compound that could be related to [Y]. Malonic acid (C₃H₄O₄) when dehydrated can yield a compound that has a carbon skeleton similar to [Y].
- **Thermal Decomposition of Carbon Suboxide**: This method produces carbon dioxide and other products but does not directly relate to the formation of [Y].
- **Action of Concentrated HNO₃ on Charcoal**: This method can produce various nitrogen oxides and carbon compounds, which may not directly lead to [Y].

6. **Conclusion**:
- Based on the analysis, the dehydration of malonic acid with P₂O₅ is a plausible method for preparing [Y]. Therefore, the correct answer is the first option.

### Final Answer:
Y may be prepared by the dehydration of malonic acid with P₂O₅.