Thank you for the opportunity to help you with your question!
C. Yes. They have the same molecular formula, but the atoms are bound together in different way. Hexane is a straight chain hydrocarbon: all the carbon atoms are bound to each other in sequence, with no branching: no carbon atom is bound to more than 2 others. Neohexane is branched: one of the carbon atoms is bound to 4 others. (parallel with branches on trees)
D By fractional distillation: the neohexane will distill off first and can be collected separately from the hexane.
Please let me know if you need any clarification. I'm always happy to answer your questions.