Which of the following groups can be found on a chiral carbon?

A chiral carbon is defined as a carbon atom that is bonded to four different substituents. This unique arrangement gives rise to chirality, meaning that the molecule can exist in two non-superimposable mirror images known as enantiomers. The presence of four different substituents ensures that the spatial arrangement around the carbon atom lacks symmetry, which is crucial for creating distinct optical isomers that can rotate plane-polarized light in different directions.

In contrast, having two identical substituents would create a plane of symmetry, making the carbon achiral. Having only one substituent would not allow for chirality since the carbon requires four total bonds to establish its chiral nature. Finally, having four identical substituents would also result in an achiral carbon, as there would be no variation in the substituents around the carbon atom, thus negating the concept of chirality.

Therefore, the distinction in the substituents is what defines chirality in a carbon atom, leading to the conclusion that the only valid arrangement for a chiral carbon is one with four different substituents.