Step 1: Understanding optical activity of amino acids.
All naturally occurring \(\alpha\)-amino acids, except for glycine, are optically active because they contain a chiral carbon atom (except glycine which has two hydrogen atoms on the chiral center, making it achiral).
Step 2: L-configuration of amino acids.
Most naturally occurring amino acids are in the L-configuration, which is why they are optically active (except glycine).
Step 3: Conclusion.
Thus, both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A), making option (A) the correct answer.