Bleaching powder dissolves in water to form .
A. $Ca{(OH)_2},C{l_2}$
B. $C{a^{ + 2}},C{l^ - },Cl{O^ - }_2$
C. $C{a^{2 + }},Cl,Cl{O^ - }_3$
D. $C{a^{2 + }},C{l^ - },Cl{O^ - }_4$

Hint: Bleaching powder has the chemical formula $Ca{(OCl)_2}$ and its chemical name is calcium hypochlorite as it contains $OC{l^ - }$ group . It is soluble in water means it reacts with water and forms new compounds .

Complete step by step answer:
Bleaching powder is prepared by reacting dry slaked lime with chlorine gas .
When we react with bleaching powder with water we obtain the following equation .
$Ca{(OCl)_2} + {H_2}O \to Ca{(OH)_2} + C{l_2}$
From the above reaction we can see that when bleaching powder reacts with water calcium hydroxide and chlorine gas is produced .

Hence , option A is correct .

Additional Information:
Bleaching powder is a white powder with a strong smell of chlorine , soluble in cold water . It can react with dilute acids and produces chlorine as a product , if we treat it with excess dilute acid all the chlorine will be liberated , thus we may infer that the bleaching agent in bleaching powder is chlorine .
Bleaching powder has various uses in real life .
It is used to sanitize public swimming pools and disinfect drinking water .
It is also used in organic chemistry as it is a very good oxidising agent .
It is also used as a bleaching agent in the textile industry to bleach dirty clothes .

Note:
When chlorine gas reacts with dry slaked lime bleaching powder is formed . The equation for same is as below :
$2Ca{(OH)_2} + 2C{l_2} \to Ca{(OCl)_2}$
Therefore , the actual composition of bleaching powder is $Ca{(OCl)_2}.CaC{l_2}.Ca{(OH)_2}.2{H_2}O$