Which of the following DOES NOT represent the appropriate hybridization state of
the carbon atoms in the structures shown below?

(1) H--CN ; sp hybridized
(2) CH3(+) ; sp3 hybridized
(3) H2C==CH2 ; sp2 hybridized
(4) O=C=S ; sp2 hybridized

What do you think the answer is, and why would to be inclined to pick that answer?

I think . It's 4.
Why you are declined to answer?