Which of the following is not chiral?

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 $Br_2/CCl_4$.

Optically active $(S)-2-$methoxypropanal on reaction with $MeMgX$ gives a mixture of alcohols. The major diastereomer $P$ on treatment with $MeI / K_2CO_3$ gives an optically inactive compound. $P$ is

Lactic acid shows which type of isomerism?

How many optically active stereoisomers are there for butane-$2,3$-diol?

Calculate the enantiomeric excess of a mixture containing $6 \ g$ of $(+)-2$-butanol and $4 \ g$ of $(-)-2$-butanol.