Question

Which is S-lactic acid among the two isomers?

• A. $a$
• B. $b$
• C. Both $a$ and $b$
• D. None of above

Answer 1

The correct option is A $a$

Lactic acid is chiral, consisting of two optical isomers. One is known as $L-(+)$-lactic acid or $\left(S\right)-$lactic acid and the other, its mirror image, is $D-\left(\right)-$lactic acid or $\left(R\right)$-lactic acid. $\left(S\right)$-lactic acid is dextrorotatory. (a) is dextrorotatory isomer of lactic acid and hence it is the right option.