Potassium permanganate (KMnO₄) is used for purifying drinking water mainly because it acts as which of the following?

Introduction / Context:
Potassium permanganate (KMnO₄) is a dark purple compound commonly used in laboratories and in household water treatment in small quantities. It appears in general science questions because of its strong chemical properties and its use in disinfection. Understanding whether it acts as an oxidising or reducing agent and how that relates to water purification is important for both chemistry and everyday awareness of safe water practices.

Given Data / Assumptions:

• The question asks why potassium permanganate is used to purify drinking water.
• Options describe it as a sterilising agent, impurity dissolver, reducing agent, oxidising agent, or None of the above.
• We assume low, controlled doses of KMnO₄ added to water to kill germs and oxidise contaminants.

Concept / Approach:
Chemically, potassium permanganate is a powerful oxidising agent. An oxidising agent is a substance that accepts electrons from other species, thereby oxidising them. In water treatment, KMnO₄ oxidises organic matter, iron, manganese, and some microorganisms, helping to remove odours and kill pathogens. While we may casually say that it sterilises water, the underlying reason is its oxidising power. Therefore, the correct conceptual answer is that it is an oxidising agent, which in turn provides a sterilising effect.

Step-by-Step Solution:
Step 1: Recall that in redox chemistry, KMnO₄ is almost always cited as a classic oxidising agent. Step 2: In aqueous solution, permanganate ions (MnO₄⁻) accept electrons and get reduced, while other substances are oxidised. Step 3: When added to water, KMnO₄ helps oxidise organic impurities and can damage cell walls of microorganisms, effectively disinfecting the water. Step 4: The phrase dissolves impurities is misleading because the main action is chemical oxidation, not simple dissolution. Step 5: Hence, the best answer is that potassium permanganate is used because it is an oxidising agent.

Verification / Alternative check:
Textbooks and practical manuals mention KMnO₄ in titrations as a standard example of a strong oxidising agent. Water treatment literature also describes its use in oxidising iron and manganese in groundwater. It is never described as a reducing agent in these contexts. While some sources may informally call it a sterilising agent, that term describes the effect, not the chemical property. Exam oriented questions generally expect the precise chemical term oxidising agent as the answer.

Why Other Options Are Wrong:
A sterilising agent: Describes the effect but does not capture the specific chemical nature that exams are testing. It dissolves impurities of water: Incorrect because the key process is oxidation, not mere dissolution. A reducing agent: Opposite of its real behaviour; KMnO₄ is well known as an oxidiser, not a reducer. None of the above: Incorrect because oxidising agent is explicitly listed and is the correct concept.

Common Pitfalls:
Some students choose sterilising agent because they think in everyday terms instead of chemical terminology. Others may be unsure of the difference between oxidising and reducing agents. To avoid such mistakes, remember that in most school level examples KMnO₄, K₂Cr₂O₇, and concentrated nitric acid are strong oxidising agents. Linking potassium permanganate with oxidation, disinfection, and colour changes in titrations helps fix this concept.

Final Answer:
Potassium permanganate is used to purify drinking water mainly because it acts as an oxidising agent.