Specify which hybrid orbitals are used by carbon atoms in the following species.

(a) CSe2


(b) CO


(c) CN-

Se=C=Se
Se has a σ bond and a π bond. It's hybridization is sp2 + p
C has two σ bonds and two π bonds. It's hybridization has to be sp + p + p.
(the p orbitals are used to form the π bonds.)

:C≡O:
Both the C and the O have one σ bond and two π bonds. Each π bond requires a p orbital to the C and the O will be sp + p + p.

:C≡N:- same as CO above.