Which of the following is True for conformational isomerism?

Why is it not possible to separate and isolate different conformational isomers of ethane?

The most stable conformation of cyclohexane is: 

The boat conformation of cyclohexane is not a very stable form due to:

What is the isomerism due to the rotation an $\mathrm{C}-\mathrm{C}$ single bond called?