The theory of strain less ring was explained by

A) Baeyer

B) Sachse and Mohr

C) Kekule

D) Erlenmeyer

Strain theory, proposed by the chemist Adolf von Baeyer, explains the stability of carbocyclic compounds (compounds that contain one or more rings of carbon atoms). According to this theory, the stability of these compounds depends on the deviation of the bond angles from the ideal values observed in compounds without such rings.

The strain in these compounds can be calculated by determining how much the angles between the chemical bonds deviate from the normal bond angles. The greater the deviation, the higher the strain, and thus the less stable the ring is.

Von Baeyer suggested that carbocyclic rings are planar, meaning that in three-membered and four-membered rings, strain is more prominent. In larger rings (such as six or more atoms), the strain increases as the size of the ring increases. However, the least strain occurs in rings with five carbon atoms, such as cyclopentane, where the bond angles are closer to ideal.

Conclusion: Therefore, according to strain theory, the most stable carbocyclic ring is cyclopentane (five-membered ring), with bond angles closest to the ideal.

Hence, the correct option is option A.