What is the increasing order of stability of dihalides of $Si$,$Ge$,$Sn$,and $Pb$?

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:

Which of the following is a three dimensional silicate?

Helium mixed with oxygen is used in the treatment of

The catenation tendency of $C$,$Si$ and $Ge$ is in the order $Ge < Si < C$. The bond energies (in $kJ \ mol^{-1}$) of $C-C$,$Si-Si$ and $Ge-Ge$ bonds,respectively,are:

What is the correct order of melting temperature of $C$, $Si$, $Ge$?