How many meso isomers of $C_4H_8Cl_2$ are possible?

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 $Br_2/CCl_4$.

Which of the following compounds is not chiral?

If $n$ is the number of asymmetric carbon atoms,the number of optical isomers possible is given by the formula:

Which of the following compounds exhibits stereoisomerism?

Provide detailed information about the relationship between optical activity and molecular structure.