Step 1: Understanding the Concept
Oxidation means loss of electrons, or an increase in oxidation number.
Step 2: Oxidation numbers of sulphur
In \(\text{H}_{2}\text{S}\), S is \(-2\). In \(\text{SO}_{2}\), S is \(+4\). In elemental S, it is 0.
Step 3: Result
In \(\text{H}_{2}\text{S}\), sulphur goes from \(-2\) to 0, so it loses electrons and is oxidised.
In \(\text{SO}_{2}\), sulphur goes from \(+4\) to 0, so it is reduced. Hydrogen stays at \(+1\).
Final Answer:
Hydrogen sulphide is the substance that is oxidised.
\[ \boxed{\text{(A) }\text{H}_{2}\text{S}} \]