Optical activity of an enantiomeric mixture is $+12.6^{\circ}$ and the specific rotation of $(t)$ isomer is $+30^{\circ}$. The optical purity is $........\%$
$CH_3 - CHCl - CH_2 - CH_3$ has a chiral centre. Which one of the following represents its $R-$configuration ?
Total number of substituent present in the above compound
Number of optical isomers possible for $2$ - chlorobutane..........
Which of the following is a meso compound ?