# What is the molecular formula for hexane, cyclohexane, and toluene?

n-Hexane has six carbons and is a saturated hydrocarbon. It is the most simple compound of the three. As a straight-chained alkane, it has the general formula ${\text{C"_n "H}}_{2 n + 2}$ to account for terminal hydrogens. So, it must be ${\text{C"_6"H}}_{14}$.
Cyclohexane is simply the same compound as a ring, giving it a general formula of ${\text{C"_n "H}}_{2 n}$. So then it is just ${\text{C"_6"H}}_{12}$ to account for the absence of terminal hydrogens.
Toluene is the "common" name for methylbenzene. Benzene is ${\text{C"_6"H}}_{6}$, so methylbenzene adds ${\text{CH}}_{3}$ and takes away one $\text{H}$, making it ${\text{C"_7"H}}_{8}$; or better, ${\text{C"_6"H"_5"CH}}_{3}$.