The elements with the following atomic numbers belong to the same group:

The oxide of a metal $(R)$ can be reduced by the metal $(P)$,and metal $(R)$ can reduce the oxide of metal $(Q)$. Then the decreasing order of the reactivity of metals $(P)$,$(Q)$,and $(R)$ with oxygen is:

Which one of the following is the most electropositive element?

Which of the following is the correct order of acidic strength?

Which one of the following represents the electronic configuration of the most electropositive element?

An element $A$ dissolves in both acid and alkali. It is an example of