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

(N/A) $(i)$ Plane polarised light: When ordinary light is passed through a Nicol prism,light vibrating in a single plane is obtained. This is known as plane polarised light.
$(ii)$ Optical activity: When plane polarised light is passed through a solution of certain compounds,the light is rotated either clockwise or anticlockwise. This property is known as optical activity. Compounds rotating light clockwise are dextrorotatory ($d$-form,$+$),and those rotating it anticlockwise are laevorotatory ($l$-form,$-$).
$(iii)$ Chirality: An object that cannot be superimposed on its mirror image is called chiral. $A$ molecule is chiral if it lacks a plane of symmetry and is non-superimposable on its mirror image.
$(iv)$ Chiral centre: $A$ carbon atom bonded to four different groups is called a chiral centre or stereocentre.
$(v)$ Enantiomers: Stereoisomers that are non-superimposable mirror images of each other are called enantiomers.
$(vi)$ Diastereomers: Stereoisomers that are not mirror images of each other are called diastereomers.
$(vii)$ Meso compounds: $A$ compound containing two or more chiral centres but possessing an internal plane of symmetry,making it optically inactive,is called a meso compound.
$(viii)$ Plane of symmetry and Achiral molecule: $A$ plane of symmetry is an imaginary plane that divides a molecule into two identical halves. $A$ molecule with a plane of symmetry is achiral (superimposable on its mirror image).
$(ix)$ Centre of symmetry: $A$ point in a molecule such that any line drawn through it meets identical atoms or groups at equal distances on both sides.