What is structural isomerism? Give two examples of chain isomerism in alkanes. Or,explain the isomerism of alkanes having more than three carbon atoms using two examples.

(N/A) Structural isomers: Compounds having the same molecular formula but different structural arrangements are known as structural isomers.
This phenomenon is known as structural isomerism.
Chain isomers: If two or more compounds have the same molecular formula but different carbon chain structures,such compounds are known as chain isomers,and this phenomenon is known as chain isomerism. Alkanes having more than three carbon atoms exhibit chain isomerism.
Example-$1$: Butane $(C_4H_{10})$ has $2$ structural isomers:
$(i)$ $n$-butane: $CH_3-CH_2-CH_2-CH_3$ (continuous chain).
$(ii)$ $2$-methylpropane (isobutane): $CH_3-CH(CH_3)-CH_3$ (branched chain).
Example-$2$: Pentane $(C_5H_{12})$ has $3$ isomers:
$(i)$ $n$-pentane: $CH_3-CH_2-CH_2-CH_2-CH_3$ (straight chain).
$(ii)$ Isopentane ($2$-methylbutane): $CH_3-CH(CH_3)-CH_2-CH_3$ (branched chain).
$(iii)$ Neopentane ($2,2$-dimethylpropane): $CH_3-C(CH_3)_2-CH_3$ (branched chain).