Question

The real bleaching agent present in bleaching powder is:
A. Chlorine
B. Oxygen
C. CaO
D. None of the above

Answer 1

Hint: First you need to recall the chemical formula of bleaching powder and then you should try to find the chemical process which takes place during the bleaching. From there you can easily get the answer to this question.

Complete step by step answer:

First, let’s gain some knowledge of bleaching agents. Bleaching agents are compounds that are used to remove the color from substances such as textiles.
Calcium oxychloride ($CaOCl_{ 2 }$) is the formula of bleaching powder. It is considered as a mixed salt of hydrochloric acid and hypochlorous acid.
In the presence of the little amount of dilute hydrochloric acid, it gives out oxygen which acts as an oxidizing and bleaching agent. When it is treated with an excess of dilute acids, chlorine is evolved which is responsible for the bleaching action of bleaching powder. Chlorine gas($Cl_{ 2 }$) produced in this way is known as, “available chlorine” which is responsible for the bleaching action of bleaching powder. The strength of bleaching powder is estimated on the basis of available chlorine content.
$2CaOCl_{ 2 }\quad +\quad H_{ 2 }SO_{ 4 }\quad \rightarrow\quad CaCl_{ 2 }\quad +\quad CaSO_{ 4 }\quad +\quad 2HOCl$
2HOCl $\rightarrow$ 2HCl + 2[O]

Therefore, we can conclude that the correct answer to this question is option A.

Note: We should know that today most commercial bleaches are oxidizing agents, such as sodium hypochlorite (NaOCl) or hydrogen peroxide ($H_{ 2 }O_{ 2 }$) which are quite effective in "decolorizing" substances via oxidation.