The saturated formula would be C_8H_18, and thus the given formula C_8H_10 has "4 degrees of unsaturation".
And each degree of unsaturation CORRESPONDS to an olefinic bond, i.e. C=C OR a RING JUNCTION.
)
And thus the pictured "xylene", as well as any one of its other 2 isomers (which are?) could correspond to the formula. And by my count "xylene" has 8xxC-C sigma bonds, 10xxC-H sigma bonds, and, formally, 3xxC-C pi bonds.........
By joining and fusing rings, we could form a structure where the distinction between sigma and pi bonds are less ambiguous, however, these would be less common structures than the benzene derivative.
Note that the "degree of unsaturation" is a very useful criterion with which to assess organic molecules.
