Which of the following is optically active?

The two enantiomers of secondary butyl chloride differ from each other in which one of the following properties?

$CH_3 - CHCl - CH_2 - CH_3$ has a chiral center. Which one of the following represents its $R$-configuration?

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

Which of the following contains an asymmetric centre?

$(+)$ $2-$Methylbutan$-1-$ol and $(-)$ $2-$Methylbutan$-1-$ol have different values for which property?