An allotrope of carbon which exhibits only two types of $C-C$ bond distances of $143.5 \text{ pm}$ and $138.3 \text{ pm}$, is $....$

Among the following,the correct statements are:
$I$. Germanium exists only in traces.
$II$. $PbF_4$ molecule is tetrahedral in shape.
$III$. $GeX_2$ is more stable than $GeX_4$.

Which of the following statements are correct?
$i$. The basic structural unit of silicates is $SiO_4^{4-}$
$ii$. Silicones are biocompatible
$iii$. Producer gas contains $CO$ and $N_2$
The correct option is

The products formed when gaseous $HCl$ is passed into an aqueous $Na_2SO_3$ solution are:

Monosilane,on coming in contact with air,burns with a luminous flame producing vortex rings. These rings are of:

Which of the following pairs of elements form amphoteric oxides?