Question

why CO2 is a gas and SiO2 is a solid?

Answer 1

because at room temperature their atomic property is different

Answer 2

Only very weak dispersion intermolecular forces hold the molecules together andCO2 is a gas at room temperature. SiO2 is a network covalent solid. Each silicon makes four bonds by making four Si-O single bonds. The covalent network leads to a very strongly bonded solid with a very high melting point

hope it helps .....