Which of the following represent a pair of enantiomers?

The total number of stereoisomers possible for $2,3-dichlorobutane$ is:

Which of the following compounds is optically active?

Which of the following represent$(s)$ the enantiomer of $Y$?

Explain the following terms:
$(i)$ Plane polarised light
$(ii)$ Optical activity
$(iii)$ Chirality
$(iv)$ Chiral centre (atom)
$(v)$ Enantiomers
$(vi)$ Diastereomers
$(vii)$ Meso compounds
$(viii)$ Plane of symmetry and Achiral molecule
$(ix)$ Centre of symmetry

The total number of stereoisomers of the product formed in the reaction $CH_3-CH=CH-COOH \xrightarrow{Br_2} \text{Product}$ is: