c
\((c)\) First . of all, there are two different dimethylcyclohexanes. One has both  methyl substituents on the same side of the cyclohexane ring; it is the cis isomer (cis is Latin for "on this side"). The other has the two methyl  substituents on opposite sides of the ring ; it is the trans isomer (trans is Latin  for "across"). \(cis-1, 4\) -dimethylcyclohexane and \(trans -1, 4\) - dimethylcyclohexane are called geo"metric isomers of cis-trans stereoisomers -  they have the same atoms, and the atoms are linked in the same order, but they  differ in the spatial (stereo)  arrangement of the atoms.

First we will determine which of the two chair conformers of \(cis- 1, 4\) - dimethylcyclohexane is more stable. One chair conformer has one methyl group  in an equatorial position and one methyl group in an axial position. The  other chair conformer also has one methyl group in an equatorial position and  one methyl group in an axial position. Therefore, both chair conformers are  equally stable.