Option 1 is the right answer.
Bleaching Powder is a chemical compound with formula Ca(ClO)2. (Calcium hypochlorite). It is widely used for water treatment. It is used for disinfection of water in the treatment process. The chlorine released by the Bleaching powder kills Pathogens (Disease causing Bacteria). The residual effect of this chlorine protects water from getting infected / contaminated with pathogens.