Which of the following are enantiomers?

Which of the following pairs of $2,3-$butanediol are enantiomers?

Which of the following is the erythro form and optically active?

Which of the following compounds exhibits stereoisomerism?

Which of the following compounds may not exist as enantiomers?

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