Which of the following is true for the stereochemical relationship of the given structures (A-D)?

Step 1: Stereochemistry Analysis.
Structures (A) and (D) are stereoisomers that are not mirror images, differing in the spatial arrangement around a chiral center. This classifies them as diastereomers.
Step 2: Conclusion.
Therefore, option (4) is correct because (A) and (D) are diastereomers. The other options incorrectly describe stereochemical relationships.
Final Answer: \[\boxed{\text{(4) (A) and (D) are diastereomers}}\]
(a) Define the following:
(i) Enantiomers
(ii) Racemic mixture
Assertion (A): All naturally occurring \(\alpha\)-amino acids except glycine are optically active. Reason (R): Most naturally occurring amino acids have L-configuration.

