Which of the following cycloalkane conformations is characterized by minimal angle strain and torsional strain, making it the most stable form?

The most stable cycloalkane conformation is the chair form of cyclohexane, because it keeps each C–C–C angle close to 109. 5° and avoids eclipsing bonds. In the chair, each carbon is sp³ hybridized, so the bond angles match the tetrahedral ideal and no bonds are forced into a higher-energy arrangement. Torsional strain is eliminated because the hydrogens on adjacent carbons are staggered, not eclipsed. For example, in the chair, a hydrogen on one carbon points away from the neighboring carbon’s hydrogen, keeping the molecule relaxed and energetically favorable.