Which types of isomerism is shown by 2,3-dichlorobutane?

Benzene and toluene form nearly ideal solutions. At 20 ^oC, the vapour pressure of benzene is 75 torr and that of toluene is 22 torr. The partial vapour pressure of benzene at 20 ^oC for a solution containing 78 g of benzene and 46 g of toluene in torr is

Equimolar solutions in the same solvent have

Amongst the following the most basic compound is