Calculate the degree of unsaturation that corresponds to each of the following molecular formulas. (a) $\mathrm{C}_{7} \mathrm{H}_{12} ;$ (b) $\mathrm{C}_{8} \mathrm{H}_{7} \mathrm{NO}_{2} ;$ (c) $\mathrm{C}_{6} \mathrm{Cl}_{6} ;$ (d) $\mathrm{C}_{10} \mathrm{H}_{22} \mathrm{O}_{11} ;$ (e) $\mathrm{C}_{6} \mathrm{H}_{10} \mathrm{~S}$;
(f) $\mathrm{C}_{18} \mathrm{H}_{28} \mathrm{O}_{2}$.