The stability of dihalides of $Si$,$Ge$,$Sn$ and $Pb$ increases steadily in the sequence

The group $14$ elements $A$ and $B$ have the first ionisation enthalpy values of $708$ and $715 \ kJ \ mol^{-1}$ respectively. These values are the lowest among their group members. The nature of their ions $A^{2+}$ and $B^{4+}$ respectively is:

Under hydrolytic conditions,the compounds used for preparation of linear polymer and for chain termination,respectively,are

Which of the following species is not stable?

Explain the origin and sources of group $14$ elements.

Which set of elements form electron precise hydrides?