Chain and position isomers of C5H11CL

I'm really struggling to identify chain and position isomers of C5H11Cl,

I understand that chain isomerism - Carbon atoms are rearranged
Position isomerism - Functional group is in a new position

How do I identify the functional groups?

I have found this link which identifies the isomers of C5H11Cl: https://www.chegg.com/homework-help/draw-eight-constitutional-isomers-molecular-formula-c5h11cl-chapter-7-problem-47p-solution-9780077354725-exc

However, I'm struggling to identify which display chain and position isomerism. Is the function group Cl?

Functional group is the chloro group R-Cl. So positional isomerism is when you change position of the Cl

I see,

so 1 and 3 could be positional isomerism. Looking at the structures on the link, are 7, 8 and 5 considered chain isomerism due to the CH3 being in different positions?

No 7,8,5 are positional isomers. In each, there is one methyl group branching out. The only difference is the position of the chloro group [chlorine atom]
1,3 are also positional isomers.

So, 2,4 and 6 are chain isomers? Is this simply due to the different carbon skeletons?