Question

What happens when chlorine water is exposed with sunlight?
A) Light yellow colour becomes colourless
B) Light yellow colour becomes dark yellow
C) Light yellow colour becomes faint green
D) No change in colour

Answer 1

Hint:. Chlorine water or chlorinated water is light yellow in colour. When chlorine water is exposed to sunlight, chlorine reacts with water to form hypochlorous acid (HClO) and further, hypochlorous acid breaks down into hydrochloric acid and oxygen gas.

Complete step by step answer:
Chlorine water solution is formed by dissolving chlorine in water and it is naturally light yellow in colour. But when chlorine water is exposed to sunlight, the chlorine ($C{l_2}$) reacts with water molecules in the presence of sunlight and forms hypochlorous acid (HClO). Further this HClO undergoes decomposition and gets separated into nascent oxygen (O) and hydrochloric acid (HCl). This complete process can be shown with chemical reactions as:
$C{l_2} + {H_2}O \rightleftharpoons HClO + HCl$

Further, decomposition of HClO:
$HClO \to HCl + [O]$ (nascent oxygen)
$[O] + [O] \to {O_2}$ (oxygen gas)
So, we get oxygen gas and hydrochloric acid as products. Oxygen gas is odourless and colourless gas. Therefore, we can say that when chlorine water, having characteristic light yellow colour is exposed with sunlight, it produces colourless gas or becomes colourless from light yellow.
So, the correct answer is “Option A”.

Additional Information:
The process of addition of chlorine or chlorine compounds to water is called water chlorination. This method is adopted to kill viruses, bacteria and other microbes in water. Basically, chlorination is done to prevent the spread of common waterborne diseases such as typhoid, cholera and dysentery.

Note: Chlorine ($C{l_2}$) is a highly effective disinfectant known and is also a very strong oxidising agent. It kills organic molecules present in impure water via the oxidation. Chlorine and hypochlorous acid are not charged and thus easily penetrate the negative charged surface of microbes.