When $16.8 ext{ g}$ of white solid $X$ were heated, $4.4 ext{ g}$ of acid gas $A$ that turned lime

Question

When $16.8	ext{ g}$ of white solid $X$ were heated, $4.4	ext{ g}$ of acid gas $A$ that turned lime water milky was driven off together with $1.8	ext{ g}$ 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 effervesced with acid giving off carbon dioxide.

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