Silicon dioxide is formed by the reaction of:

Choose the correct statements about allotropes of carbon:
$I$. Graphite has a layered structure.
$II$. Buckminsterfullerene is not aromatic in nature.
$III$. The distance between two adjacent layers in graphite is $340 \ pm$.
$IV$. The hybridization of carbons in graphite and Buckminsterfullerene is the same $(sp^2)$.

$RCl$ $\xrightarrow[Si]{Cu \text{ powder}} R_2SiCl_2$ $\xrightarrow{H_2O} R_2Si(OH)_2$ $\xrightarrow{\text{condensation}} A$
Compound $(A)$ is:

Which of the following elements exhibit metallic nature among $C$,$Si$,$Ge$,$Sn$,and $Pb$?

Pyrosilicate ion is

Correct statements among $(i)$ to $(iv)$ regarding silicones are:
$(i)$ they are polymers with hydrophobic character
$(ii)$ they are biocompatible
$(iii)$ in general,they have high thermal stability and low dielectric strength
$(iv)$ usually they are resistant to oxidation and used as greases.