Among the following options, the element with the highest density and lowest boiling point is

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:

Identify the correct statements from the following.
$(i)$ Quartz is a piezoelectric material.
$(ii)$ All group $14$ tetrachlorides except $CCl_4$ are easily hydrolyzed in water.
$(iii)$ The $C-C$ bond distance within the layer of graphite is $154 \ pm$.
$(iv)$ $SiO_2$ is soluble in aqueous $HCl$ solution.

Which set of elements form electron precise hydrides?

Which of the following oxides is amphoteric in nature?

$[SiF_6]^{2-}$ is known whereas $[SiCl_6]^{2-}$ is not. Give possible reasons.