$\alpha$-hydroxy propanoic acid has $..........$ asymmetric carbon atoms.

Which of the following pairs of $2,3-$butanediol are enantiomers?

Which of the following compounds might be useful to the chemist trying to increase the optical purity of the $(d)$ sample?

In the reaction sequence shown below,determine the total number of stereoisomers formed as the final product $D$. The starting material is $CH_3-CD(CH_3)-C \equiv C-CO-CH_3$. The reaction $A$ is $LiAlH_4$ (or similar reducing agent to reduce the alkyne to a cis-alkene),$C$ is the cis-isomer,and the final step is the addition of $Br_2/CCl_4$.

What does the given structure represent?

Which of the following acids does not exhibit optical isomerism?