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 with the nitrites to form a purple color. The intensity of the purple color is proportional to the concentration of nitrites in the sewage.

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.