Answer: The correct answer is Option 2.
Step-by-step explanation:
For the given options:
Option 1: Hydroxide ion
The chemical formula for this ion is

Option 2: Hydronium ion
The chemical formula for this ion is

Option 3: Hypochlorite ion
The chemical formula for this ion is

Option 4: Perchlorate ion
The chemical formula for this ion is

For the given chemical reaction:

The ion represented by X is hydronium ion.
Hence, the correct answer is Option 2.