CBSE 2025, Set 1

Question

**Assertion (A):** All naturally occurring $\alpha$-amino acids except glycine are optically active.

**Reason (R):** Most naturally occurring amino acids have L-configuration. A). Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). B). Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). C). Assertion (A) is true, but Reason (R) is false. D). Assertion (A) is false, but Reason (R) is true.

Edvaya · Accepted Answer

The correct answer is Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).. **A is TRUE:** Glycine (H$_2$NCH$_2$COOH) has no chiral centre (two identical H on $\alpha$-carbon) — optically inactive. All other $\alpha$-amino acids are optically active. **R is TRUE:** Naturally occurring amino acids predominantly have L-configuration. **R does not explain A** — optical activity arises from having a chiral carbon, not from L-configuration per se. Both true, but R is not the correct explanation.

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