The number of six-membered and five-membered rings in Buckminster fullerene respectively is

Explain the following:
$(a)$ $CO_2$ is a gas whereas $SiO_2$ is a solid.
$(b)$ Silicon forms $SiF_6^{2-}$ ion whereas corresponding fluoro compound of carbon is not known.

The basic building unit of all silicates is

$A$ red solid is insoluble in water. However,it becomes soluble if some $KI$ is added to water. Heating the red solid in a test tube results in the liberation of violet-coloured fumes and droplets of a metal appear on the cooler parts of the test tube. The red solid is:

What is the product formed in the reaction $SnO_2 + HCl$ (excess)?

Identify the species,which does not exist?