Statement-I : It has not been possible to separate and isolate different conformational isomers of ethane.

Statement-II : The energy difference between the two extremes forms of ethane is of the order of $12.5\mathrm{kJ}{\mathrm{mol}}^{-1}$

The staggered conformation of ethane is more stable than eclipsed conformation. Since eclipsed conformation has a greater potential energy due to torsional strain, it is less stable than the staggered conformation.

Staggered and eclipsed forms differ by 12.5 kJ / mol

No, eclipsed and staggered conformations of ethane cannot be isolated. It is because of very small energy difference between these two conformations.