$Sodium$ metal is highly reactive and cannot be stored under:

Magnitude of which of the following property of alkali metals increases with the increase of atomic number?

$Na + Al_2O_3$ $\xrightarrow{\text{High temperature}} X$ $\xrightarrow[\text{water}]{CO_2} Y$; compound $Y$ is

Among the statements $(a)-(d)$ the correct ones are
$(a)$ Lithium has the highest hydration enthalpy among the alkali metals.
$(b)$ Lithium chloride is insoluble in pyridine.
$(c)$ Lithium cannot form ethynide upon its reaction with ethyne.
$(d)$ Both lithium and magnesium react slowly with $H_2O$.

Give the use of hydrated zeolites.

Caesium is used in