Stereoisomers

Concept: Enantiomers are non-superimposable mirror images with opposite configuration at all chiral centres.

Step 1: Identify chiral centres in each pair. Check for chiral carbons and arrangement of substituents (wedge/dash).

Step 2: Compare configurations. In options (A), (B), and (C): structures are either identical or diastereomers (differ at some but not all chiral centres).

Step 3: Check option (D). All chiral centres are inverted — structures are exact mirror images and non-superimposable.