Which alkali metals are useful as electrodes in photoelectric cells?

$A$ metal $X$ on heating in a stream of nitrogen gives $Y$. $Y$ on reaction with ${H_2}O$ gives a colorless gas which,when passed through a $CuSO_4$ solution,gives a blue color. What is $Y$?

Which of the following metals forms an amphoteric oxide?

Give reasons: Aluminium utensils should not be kept in water overnight.

The chloride of an element gives a neutral solution in water. To which group of the periodic table does this element belong?

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