The correct answer is option 1: Copper sulphate. Copper sulphate is commonly used as a fungicide in water treatment processes to eliminate fungi in water tanks. It is an effective and widely used chemical due to its antifungal properties. Copper ions from copper sulphate bind with proteins and enzymes in fungi, disrupting their cell membranes and damaging their DNA, ultimately killing them. It is particularly effective against filamentous fungi, such as those found in water tanks.

Alert - correct answer should be Calcium hypochlorite. Calcium hypochlorite is commonly used to destroy fungi in water tanks. It is a strong oxidizing agent that generates hypochlorous acid, a powerful disinfectant, upon dissolving in water. Hypochlorous acid effectively kills fungi by attacking their cell walls and interfering with their metabolic processes. Calcium hypochlorite is widely used for its high efficiency in eliminating various types of harmful microorganisms, including fungi, bacteria, and algae.