Both the statements are individually true, but Statement II is not the correct explanation of Statement I. A solar day is the timeit takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky. The sidereal day is the time it takes for the Earth to complete one rotation about its axis with respect to the 'fixed' stars. Sidereal day is 23 hours, 56 minutes and 4.1 seconds. The average solar day is defined as 24 hours long. Hence, the sidereal day is ~4 minutes shorter than the solar day. Statement II is factual as the motion of the Earth in its orbit around the Sun is termed as revolution.