Question

Which formula represents propyne?
(1) C3H4 (3) C5H8
(2) C3H6 (4) C5H10

Answer 1

(1) C3H4 is the correct answer.
Hope this helps~

Answer 2

Propyne is an alkyne which has the general formula CnH(2n-2)

Prop- sets the value of n to 3.

So the formula is C3H(2*3-2) which is C3H4, therefore the answer is 1.
For general trivia I do believe the structure of it is CH3C triple bonded to CH, although I could be wrong.