Explanation:
When hydrogen sulfide (H2S) is present in water, it can be oxidized into sulfate (SO4^2-) through a process called chlorination. Chlorination involves the addition of chlorine (Cl2) or a chlorine-containing compound to the water to oxidize the H2S.

Here is a detailed explanation of how chlorination converts hydrogen sulfide into sulfate:

1. Introduction to chlorination:
Chlorination is a commonly used method for disinfection and oxidation in water treatment. It involves the addition of chlorine or a chlorine-containing compound to water to kill bacteria, viruses, and other microorganisms, as well as to oxidize certain impurities.

2. Oxidation of hydrogen sulfide:
When chlorine is added to water containing hydrogen sulfide, it reacts with H2S to form sulfurous acid (H2SO3) and hydrochloric acid (HCl):

H2S + Cl2 → H2SO3 + 2HCl

Sulfurous acid is a weak acid that further reacts with oxygen in the presence of chlorine to form sulfuric acid (H2SO4):

H2SO3 + ½O2 → H2SO4

3. Formation of sulfate ions:
Sulfuric acid (H2SO4) is a strong acid that readily dissociates in water to release hydrogen ions (H+) and sulfate ions (SO4^2-):

H2SO4 → 2H+ + SO4^2-

The sulfate ions formed in the reaction contribute to an increase in the concentration of sulfates in the water.

4. Importance of sulfate stabilization:
Stabilizing sulfates in water is essential to prevent the formation of undesirable by-products such as hydrogen sulfide gas, which is responsible for unpleasant odors and corrosion issues. By oxidizing hydrogen sulfide into sulfate, chlorination helps to eliminate these problems and ensure the water is safe and free from odor.

Therefore, the correct answer is option 'A': Chlorination.