Which of the following compounds is an optically active compound?

Identify chiral molecules from the following:

Which of the following compounds are optically active?
$(I)$ $1,1-$dimethyl$-4-$chlorocyclohexane
$(II)$ $4-$chlorocyclohex$-1-$ene
$(III)$ penta$-2,3-$diene

Number of optical isomers possible for $2$-chlorobutane is:

Meso-tartaric acid is

The maximum number of possible optical isomers in $1-$bromo$-2-$methylcyclobutane is