NCERT Exemplar Solutions Class 7 Science Solutions for Wastewater Story - Exercise in Chapter 18 - Wastewater Story

Question 17 Wastewater Story - Exercise

Pick from the following one chemical used to disinfect water.

(a) Chlorine

(b) Washing soda

(c) Silica

(d) Coal


The answer is (a) Chlorine.


Chlorine is a very good oxidizer. It kill pathogens and germs by breaking their bonds. This is how it disinfects water. Chlorine kills pathogens such as bacteria and viruses by breaking the chemical bonds in their molecules. Disinfectants that are used for this purpose consist of chlorine compounds which can exchange atoms with other compounds, such as enzymes in bacteria and other cells.When enzymes come in contact with chlorine, one or more of the hydrogen atoms in the molecule are replaced by chlorine.This causes the entire molecule to change shape or fall apart. When enzymes do not function properly, a cell or bacterium will die.

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