The number of isomeric structures are possible for bromopentane?

Positional isomers have the same molecular formula and functional groups but differ in the position of the substituent(s) on the carbon chain.

Chain isomers have the same molecular formula but differ in the arrangement of the carbon chain.

Stereoisomers have the same molecular formula and the same sequence of bonded atoms but differ in the spatial orientation of the atoms in three-dimensional space.
For bromopentane (C5H11Br), there are a total of 8 possible isomers:
1-bromopentane
2-bromopentane
3-bromopentane
4-bromopentane
2-methyl-1-bromopentane
3-methyl-1-bromopentane
2-methyl-2-bromopentane
2,3-dimethyl-1-bromopentane
Out of these, the first four isomers are positional isomers, while the remaining four are chain isomers. None of the isomers of bromopentane exhibit stereoisomerism since there is no carbon atom in the molecule that is attached to four different substituents.