Assertion : Staggered conformation of ethane is 12.5 ~kJ ~mol ⁻¹ more stable than the eclipsed conformation. Reason: The two conformations of ethane cannot be separated at room temperature.

Step-by-step solution

Staggered conformation is more stable because in this conformation any two hydrogen atoms on adjacent carbon atoms are as far apart as possible and the repulsion between the electron clouds of -bonds of two non-bonded hydrogen atoms is minimum. The energy difference of 12.55 ~kJ ~mol ⁻¹ is not large enough to prevent rotation at room temperature as a result it is not possible to seperate the two conformations of ethane.