Conformational isomers are structures obtained by rotation around single bonds. Conformational isomers are easily interconvertible as the energy differences are very small between the various structures. The conformation of cyclohexane which is most stable is (a) boat (b) twist boat (c) chair (d) planar

There are four possible conformations given: boat, twist boat, chair, and planar. Each of these conformations has a different arrangement of atoms due to rotations around the single bonds of the cyclohexane ring.

Torsional strain refers to the strain caused by repulsion between molecules in a chemically bonded system. Steric hindrance refers to the interference of atoms in a molecule about the bond rotamers. - Boat: This conformation has a significant torsional strain due to repulsion between hydrogen atoms on the two "ends" of the boat. There is also steric hindrance between the hydrogen atoms on the two carbons facing each other in the middle of the boat. - Twist boat: This conformation is slightly more stable than the boat conformation, as the torsional strain is reduced by twisting the boat structure. However, there is still significant steric hindrance between the hydrogen atoms on the two carbons facing each other. - Chair: This conformation has the least torsional strain and steric hindrance, as the hydrogen atoms on adjacent carbons are staggered and there is no significant steric hindrance. - Planar: The planar conformation has the maximum torsional strain as all the hydrogen atoms on the cyclohexane ring are in an eclipsed conformation. There is also significant steric hindrance.

Based on the evaluation of torsional strain and steric hindrance in step 2, it is clear that the chair conformation has the least torsional strain and steric hindrance. Therefore, the most stable conformation of cyclohexane is the chair conformation. So the correct answer is (c) chair.