In the compound 1CH2 = 2C−H|3C|H−4H|C|H−5C ≡ 6CH, the hybridization of C3 is:
Lets draw the structure again,
1CH2 = 2C−H|3C|H−4H|C|H−5C ≡ 6CH
Now , Number of hybrid oribitals = number of bonded pairs + number of lone pairs
⇒ Number of hybrid orbitals = 4
⇒ sp3 hybridization.
Therefore,the hybridization of C3 is sp3.