A compound 'X' is bitter in taste. It is used for softening hard water. It is used for manufacture of glass. It is component of washing powder. It reacts with dil. HCl to produce brisk effervescence due to colourless, odourless gas 'Y' which is non-supporter of combustion and turns lime water milky due to formation of 'Z'. When excess of CO2 is passed, milkiness disappears due to formation of 'P'. Identify 'X', 'Y', 'Z' and 'P' and write all the reaction involved.