The atomic radii of the alkali metals follow the order

Assertion $(A)$: $K$, $Rb$, and $Cs$ form superoxides.
Reason $(R)$: The stability of the superoxides increases from $K$ to $Cs$ due to the decrease in lattice energy.
The correct answer is:

What is obtained when sodium metal is heated in a stream of dry ammonia?

What is the product of the reaction between aluminium and aqueous $NaOH$?

Why is $LiF$ almost insoluble in water whereas $LiCl$ is soluble not only in water but also in acetone?

Which of the following metals does not produce the smell of ammonia when burned in moist air?