`X_(2)` is a greenish yellow gas with pungent offensive smell used in purification of water. It partially dissolves in `H_(2)O` to give a solution which turns blue litmus red. When `X_(2)` is passed through NaBr solution, `Br_(2)` is obtained.
Identify `X_(2)`, name the group to which it belongs.

Explanation

To solve the problem, we need to identify the gas \(X_2\) based on the clues provided in the question. Let's break down the information step by step.

### Step 1: Identify the characteristics of \(X_2\)
- The gas \(X_2\) is described as a greenish-yellow gas with a pungent, offensive smell.
- It is used in the purification of water.
- It partially dissolves in water to give a solution that turns blue litmus paper red.

### Step 2: Determine the nature of the solution formed
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