Question

Explain why CO2 is a gas but SiO2 is a solid

Answer 1

because SiO2 form polymer and due to polymerisation its boiling point increses .... because of this SiO2 is gas at room temp.

Answer 2

Carbon dioxide has discrete molecules and remains as a gas at room temperature because its molecules is non-polar due to its linear structure.
On the other hand, silica (SiO2), each silicon is linked to four oxygen atoms tetrahedrally and each oxygen atom linked to two sillicon atoms. Thus silica exists as a giant molecule having a three dimensional structure. Therefore, it is a solid at room temperature.