Salt Analysis

When 16.8 g of white solid X were heated, 4.4 g of acid
gas A, that turned lime water milky was driven off together
with 1.8 g of a gas B which condensed to a colourless
liquid.

The solid that remained, Y, dissolved in water to
give an alkaline solution, which with excess barium
chloride solution gave a white precipitate Z. The precipitate
efferversced with acid giving off carbon dioxide. Identify
A, B and Y and write down the equation for the thermal
decomposition of X.