The chemical used to disinfect water is (a) Chlorine.
Explanation: Chlorine is widely used to kill harmful bacteria and other microorganisms in water, making it the primary disinfectant for drinking water.
Why other options are incorrect:
(b) Washing soda: While washing soda (sodium carbonate) has cleaning properties, it is not used for water disinfection. It’s mainly used to soften water and remove grease.
(c) Silica: Silica is a mineral compound that can be used in water filtration systems to remove particles, but it is not considered a disinfectant.
(d) Coal: Coal is a fossil fuel and is not used for water disinfection.