The hydrides of which group elements of the periodic table form electron precise hydrides?

The alkali metal with lowest $E^{\circ}{ }_{M^{+} / M}(\mathrm{~V})$ is $X$ and the alkali metal with highest $E^{\circ}{ }_{M^{+} / M}(\mathrm{~V})$ is $Y$. Then $X$ and $Y$ are respectively

Assertion (A) Be and Mg do not impart any colour to the flame.

Reason (R) The electrons in them are strongly bound to get excited by flame.

Aluminium reacts with dilute HCl and liberates a gas ' $A$ ' and with aqueous alkali liberates a gas ' $B$ '. $A$ and $B$ respectively are