Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

The correct answer to this question is the same compound. An enantiomer is also known as an optical misnomer, and it is each of a pair of molecules that are mirror images of one another; these molecules are non-superimposable. Diastereomers are a type of stereoisomer, and are defined as non-mirror image non-identical stereoisomers and are also non-superimposable.

A diastereomer is any stereoisomer that is not an enantiomer. Diastereomers often have different chemical reactivity as they have different physical properties. The diagram in this question does not fit into either of these categories, so therefore it is the same compound, or answer C.