Identify the relationship between the given pair of molecules:

Which pair represents chain isomers?

The number of isomers of $C_4H_{10}$ is:

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.

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

The number of possible isomers for the molecular formula $C_2H_3Cl_3$ is...........