What is formed by the reaction of carbon dioxide with water?

$A$ compound $X$ is a constituent of baking powder. It is used as an antacid. When $X$ is heated, it releases a gas $Y$ which, when passed through lime water, turns it milky, and a salt $Z$ is formed, which is the main constituent of washing powder. Identify $X, Y$, and $Z$. Write balanced chemical equations for the reactions involved.

Why does $1 \, M \, HCl$ solution have a higher concentration of $H^{+}$ ions than $1 \, M \, CH_{3}COOH$ solution?

Explain why:
$(a)$ the colour of copper sulphate crystals changes on heating?
$(b)$ baking soda acts as an antacid?
$(c)$ an acid should be added to water while diluting?

Give three practical applications of neutralisation reaction.

To protect against tooth decay,we are advised to brush our teeth regularly. The nature of the toothpaste commonly used is: