What type of oxide is aluminium oxide $(Al_2O_3)$?

During which reaction is dihydrogen gas not produced under normal conditions?

When a metal $X$ is treated with cold water, it gives a basic salt $Y$ with molecular formula $XOH$ (molecular mass $= 40$) and liberates a gas $Z$ which easily catches fire. Identify $X$, $Y$, and $Z$, and write the chemical reaction involved.

In which of the following,is a displacement reaction possible?

An alkali metal $A$ gives a compound $B$ (molecular mass $= 40$) on reacting with water. The compound $B$ gives a soluble compound $C$ on treatment with aluminium oxide. Identify $A$,$B$ and $C$ and give the reaction involved.

During the reaction of some metals with dilute hydrochloric acid,following observations were made.
$(a)$ Silver metal does not show any change.
$(b)$ The temperature of the reaction mixture rises when aluminium $(Al)$ is added.
$(c)$ The reaction of sodium metal is found to be highly explosive.
$(d)$ Some bubbles of a gas are seen when lead $(Pb)$ is reacted with the acid.
Explain these observations giving suitable reasons.