6. Define 'positional isomer'.

They have the same molecular formula but a different arrangement of atoms in space.
They have the same structural formula and chain length, but differ in the position of their functional group.
They have the same molecular formula but different functional groups.

7. Define 'chain-branching isomer'.

They have the same molecular formula but interact differently with plane polarised light.
They have the same molecular formula but a different arrangement of the carbon chain.
They have the same molecular formula but a different structural formula.j