Why is $Meso-tartaric$ acid optically inactive?

The number of optical isomers possible for $2-$Bromo$-3-$chlorobutane are

Which of the following may exist in enantiomorphs?

Which of the following capital letters is chiral?

Which of the following isomers of $C_7H_{16}$ exhibits optical isomerism?

The well-known compounds, $(+)$-lactic acid and $(-)$-lactic acid, have the same molecular formula, $C_{3}H_{6}O_{3}$. The correct relationship between them is