Which compound produces $H_2$ gas in an aqueous solution?

The solubility of an ionic compound is compared in heavy water $(D_2O)$ and simple water $(H_2O)$. It is:

The hydride ion $H^{-}$ is a stronger base than the hydroxide ion $OH^{-}$. Which of the following reactions will occur if sodium hydride $(NaH)$ is dissolved in water?

What is $X$ in the following reaction?
$MgCl_2 + 2H_2O \to X + 2HCl + H_2O$

Consider the following statements regarding heavy water $(D_2O)$. Which of the following statements is/are correct?
$(A)$ Heavy water is used as a moderator in nuclear reactors.
$(B)$ The power of association is higher in $D_2O$ than in ordinary water $(H_2O)$.
$(C)$ Heavy water is more effective as a solvent than ordinary water.

Write chemical reactions to show the amphoteric nature of water.