The hybridisation of each carbon atom in an alkane such as ethane is

Explanation

Four sigma bonds require four equivalent orbitals, so one s and three p orbitals mix to give four sp3 hybrids pointing to the corners of a tetrahedron with bond angles of 109.5 degrees. Alkenes use sp2 with 120 degree angles and alkynes sp with a linear 180 degree arrangement. Counting the sigma bonds and lone pairs on an atom is the quickest way to assign hybridisation.