Answers

2016-03-21T21:33:22+05:30
It is because the intermolecular forces between co2 are veryweak where as between sio2 it is strong 
due to this reason one is gas where as the other one is solid
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2016-03-21T21:40:21+05:30
" the only reason for the SiO₂ to be a solid and the CO₂ to be a gas is the internal molecular force between the atom "

⇒ the internal molecular force is more in SiO₂
⇒ the internal molecular force is less in CO₂

therefore SiO₂ is a solid and CO₂ is gas
2 5 2
Hope so my answer is useful and mark as best if possible :D