Alkene family has the general formular Cn_nnH2n_{2n}2n, thus Alkene with 6 Carbon atoms is C6_66H12_{12}12, while the alkyne family has the general formula Cn_nnH2n−2_{2n-2}2n−2, thus alkyne with 6 carbon atoms is C6_66H10_{10}10.
The difference between them is the H2_22.
If H = 1, then H2_22 = 1 x 2 = 2.