Are bonds ever truly 100 % ionic or 100 % covalent and why?

No compound is 100% ionic. If the bond involves the same atoms (a homonuclear bond, A-A) then the bond must be 100% covalent because neither atom has the ability to attract the electron pair more strongly than the other. ... The reason for this is that an electron is never completely transferred from one atom to another.

porque o gás carbônico afasta o oxigênio da parte que está em chamas, e não existe fogo sem oxigênio