Sulphur on reaction with conc. `H_2SO_4` gives X which on reaction with NaOH gives Y which on further reaction with dil `H_2SO_4` give X again. Then X & Y are respectively:

Options

A. `S, Na_2SO_3`
B. `SO_2, Na_2SO_3`
C. `SO_2, Na_2SO_4`
D. `SO_3, Na_2SO_3`

Answer

To solve the problem step by step, we will analyze the reactions involving sulfur and the compounds formed during the process.

### Step 1: Reaction of Sulfur with Concentrated H2SO4
When sulfur (S) reacts with concentrated sulfuric acid (H2SO4), it is oxidized to sulfur dioxide (SO2). The balanced chemical equation for this reaction is:

\[ S + 2 H_2SO_4 \rightarrow 2 SO_2 + 2 H_2O \]

Here, the compound X formed is sulfur dioxide (SO2).

### Step 2: Reaction of X (SO2) with NaOH
Next, we take the compound X (SO2) and react it with sodium hydroxide (NaOH). This reaction produces sodium sulfite (Na2SO3) and water. The balanced equation for this reaction is:

\[ SO_2 + 2 NaOH \rightarrow Na_2SO_3 + H_2O \]

Here, the compound Y formed is sodium sulfite (Na2SO3).

### Step 3: Reaction of Y (Na2SO3) with Dilute H2SO4
Finally, we take the compound Y (Na2SO3) and react it with dilute sulfuric acid (H2SO4). This reaction produces sulfur dioxide (SO2) again, along with sodium sulfate (Na2SO4) and water. The balanced equation for this reaction is:

\[ Na_2SO_3 + H_2SO_4 \rightarrow Na_2SO_4 + SO_2 + H_2O \]

This confirms that we regenerate the compound X (SO2).

### Conclusion
From the above steps, we can conclude that:
- X is sulfur dioxide (SO2).
- Y is sodium sulfite (Na2SO3).

### Final Answer
Thus, the final answer is:
- X = SO2
- Y = Na2SO3