Consider the oxides of group $14$ elements $SiO_2$,$GeO_2$,$SnO_2$,$PbO_2$,$CO$ and $GeO$. The amphoteric oxides are

$Si_3O_9^{-6}$ (having three tetrahedral units) is represented as:

Which of the following compounds of elements in group $14$ would you expect to be most ionic in character?

Carbon and silicon both belong to group $14$, but despite the stoichiometric similarity, their dioxides (i.e., carbon dioxide and silicon dioxide) differ in their structures. Comment.

When graphite is subjected to an electric arc in the presence of an inert atmosphere,it gives:

On heating copper nitrate strongly,$.......$ is finally obtained.