When $Mg$ burns in air,it produces

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

$KO_2$ (potassium superoxide) is used in oxygen cylinders in space and submarines because it

State True or False:
$(1)$ Half-life of $^{223}Fr$ is $21 \ s$.
$(2)$ $Li^{+}$ has a high hydration enthalpy and therefore its salts are usually hydrated in nature.
$(3)$ Among all the alkali metals,only $Na$ can react with nitrogen of air and form a nitride.
$(4)$ Except $LiF$,other halides of $Li$ are soluble in water.

Which of the following compounds is obtained as a by-product in the synthesis of sodium carbonate by the Solvay process?

When sodium metal is dissolved in liquid ammonia,a blue-coloured solution is formed. The blue colour is due to: