Explain the following terms:
$(a)$ Isomerism
$(b)$ Position isomerism
$(c)$ Chain isomerism
$(d)$ Functional group isomerism
$(e)$ Metamerism
$(f)$ Optical isomerism

(N/A) Isomerism: Compounds having the same molecular formula but different physical or chemical properties due to different arrangements of atoms are called isomers,and the phenomenon is called isomerism.
$(b)$ Position isomerism: It occurs when the position of a functional group or substituent changes along the same carbon chain (e.g.,$CH_3-CH_2-CH_2-OH$ and $CH_3-CH(OH)-CH_3$).
$(c)$ Chain isomerism: It arises due to the difference in the arrangement of the carbon skeleton (e.g.,$n$-butane and isobutane).
$(d)$ Functional group isomerism: It occurs when compounds have the same molecular formula but contain different functional groups (e.g.,ethanol $CH_3CH_2OH$ and dimethyl ether $CH_3OCH_3$).
$(e)$ Metamerism: It arises due to the different distribution of carbon atoms on either side of a polyvalent functional group (e.g.,diethyl ether $CH_3CH_2-O-CH_2CH_3$ and methyl propyl ether $CH_3-O-CH_2CH_2CH_3$).
$(f)$ Optical isomerism: It is a type of stereoisomerism where isomers are non-superimposable mirror images of each other,known as enantiomers,which rotate plane-polarized light.