Choose the correct order of density of the alkali metals.

When substance $A$ reacts with water,it produces a combustible gas $B$ and a solution of substance $C$ in water. When another substance $D$ reacts with solution $C$,it produces the same gas $B$,even when reacting with dilute sulfuric acid at room temperature. $A$ gives a golden yellow flame in a Bunsen burner flame. What are $A, B, C,$ and $D$ respectively?

Write the reaction of thermal decomposition of sodium azide.

Give two uses of caustic soda.

$NaOH$ can be transported in the container made up of ?

The photoelectric effect is maximum in which of the following elements?