Can there be four bonds between the two carbon atom?

Because a quadruple bond would involve cramming 8 electrons into the same space. Such a configuration is highly unstable energetically. read more

In fact, quadruple bonds are few and far between in chemical compounds. Diatomic carbon does in fact have four pairs of electrons participating in the bond, but one of the four bonds is an antibonding orbital which is perpendicular to the plain of the axis connecting the two atoms. read more

Carbon atoms can also form double bonds in compounds called alkenes or triple bonds in compounds called alkynes. A double bond is formed with an sp 2-hybridized orbital and a p-orbital that isn't involved in the hybridization. A triple bond is formed with an sp-hybridized orbital and two p-orbitals from each atom. read more

There is now a double bond and two single bonds linked to carbon, available for sharing with another atom. Remember that a double bond equals four valence electrons. Thus, two single bonds are required to meet carbon's need of eight valence electrons (present in its outer shell) satisfied. read more