A dark violet solid X reacts with `NH_3` to form a mild explosive which decomposes to give a violet coloured gas .X also reacts with `H_2` to give an acid Y. Y can also be prepared by heating its salt with `H_3PO_4 .X and Y` are :

Options

A. `Cl_2, HCl`
B. `SO_2, H_2SO_4`
C. `Br_2,HBr`
D. `I_2, HI`

Answer

To solve the problem, we need to identify the substances X and Y based on the given reactions and properties. Let's break it down step by step.

### Step 1: Identify the Dark Violet Solid (X)
The problem states that X is a dark violet solid that reacts with ammonia (NH₃) to form a mild explosive. Among the options provided (Cl₂, SO₂, Br₂, I₂), we need to find which one is a dark violet solid.

- **Observation**: Iodine (I₂) is known to be a dark violet solid.

**Hint**: Look for the color and physical state of the substances mentioned in the options.

### Step 2: Reaction of X with Ammonia
Now, we need to consider the reaction of iodine (I₂) with ammonia (NH₃).

- **Reaction**:
\[ 3I_2 + 2NH_3 \rightarrow N_2I_3 + 3HI \]
The product N₂I₃ is a mild explosive.

**Hint**: Check the reactivity of halogens with ammonia to identify explosive compounds.

### Step 3: Decomposition of the Mild Explosive
The problem mentions that the mild explosive decomposes to give a violet-colored gas.

- **Decomposition Reaction**:
\[ N_2I_3 \rightarrow N_2 + 3I_2 + 3NH_4I \]
Here, I₂ is the violet-colored gas produced.

**Hint**: Consider the products of the decomposition reaction and their colors.

### Step 4: Reaction of X with Hydrogen (H₂)
Next, we analyze the reaction of X (I₂) with hydrogen (H₂) to form an acid Y.

- **Reaction**:
\[ H_2 + I_2 \rightarrow 2HI \]
Here, HI is hydrogen iodide, which is the acid Y.

**Hint**: Identify the products formed when halogens react with hydrogen.

### Step 5: Preparation of Y from its Salt
The problem states that Y can also be prepared by heating its salt with H₃PO₄.

- **Example**: If we take sodium iodide (NaI) as the salt of Y:
\[ NaI + H_3PO_4 \rightarrow HI + Na_3PO_4 \]
This confirms that HI can indeed be produced from its salt.

**Hint**: Look for reactions involving acids and their salts to verify the formation of the acid.

### Conclusion
From the above steps, we conclude that:
- X is I₂ (iodine)
- Y is HI (hydrogen iodide)

Thus, the answer is:
- **X = I₂**
- **Y = HI**

### Final Answer
X and Y are:
- X = I₂ (iodine)
- Y = HI (hydrogen iodide)