Which of the following compounds is optically active?

Which of the following compounds is optically active?

How many stereoisomers are possible for $2$-hydroxycyclopentanethiol?

The isomers whose structures are non-superimposable mirror images of each other are called .....

Which of the following will not show optical isomerism?

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