Question

why is carbon always double bond to oxygen

Answer 1

I would like to note that carbon and oxygen in CO are held together by triple bonds; one sigma and two pi bonds; not a double bond and in CO3, an unstable compound, the bond is not a double bond.

Answer 2

Actually carbon have 4 valence electrons in its valence shell , one single bond represents 2 electrons , so , for making the bond , We represent it as double bond , which means 4 electrons , Its just a representation & nothing else .