In the manufacture of sodium hydroxide, hydrogen gas and chlorine gas (X) are formed as by-product. Chlorine gas reacts with lime water to give bleaching powder, a bleaching agent. Thus, X is chlorine gas (Cl2) gas.
Y is calcium oxychloride or bleaching powder CaOCl2.
The equation for the preparation of sodium hydroxide is:
2NaCl (aq)+2H2O (l)Heat→2NaOH (aq)+Cl2(g)+H2(g)
Cl2(g)+Ca(OH)2(aq)→CaOCl2(aq)+H2O(l)