For detecting the nitrites in the sewage, the matching colour may be developed by adding A. Potassium permanganate B. Sulphuric acid and napthamine C. Phenol-di -sulphuric acid potassium hydroxide D. None of these

The correct answer is: A. Potassium permanganate.

Nitrites are detected in sewage by adding potassium permanganate. The potassium permanganate reacts

Sulphuric acid and napthamine are not used to detect nitrites in sewage. Phenol-di -sulphuric acid potassium hydroxide is also not used to detect nitrites in sewage.

Here is a more detailed explanation of each option:

• Option A: Potassium permanganate is a strong oxidizing agent. When it is added to sewage, it reacts with the nitrites to form a purple color. The intensity of the purple color is proportional to the concentration of nitrites in the sewage.
• Option B: Sulphuric acid and napthamine are not used to detect nitrites in sewage. Sulphuric acid is a strong acid, and napthamine is a base. When they are mixed together, they react to form a salt. This salt does not react with nitrites to form a purple color.
• Option C: Phenol-di -sulphuric acid potassium hydroxide is also not used to detect nitrites in sewage. Phenol-di -sulphuric acid is a strong acid, and potassium hydroxide is a base. When they are mixed together, they react to form a salt. This salt does not react with nitrites to form a purple color.

Therefore, the correct answer is: A. Potassium permanganate.