Final answer:
The average length of a solar day is approximately 24 hours. A solar day is determined by the time it takes for the Earth to complete one rotation relative to the Sun, taking into account the Earth's movement along its orbit.
Step-by-step explanation:
The student is asking about the average length of a solar day. A solar day is the period from one noon to the next, the time it takes for the Earth to make one full rotation on its axis relative to the Sun. A solar day is about 4 minutes longer than a sidereal day because the Earth not only rotates on its axis but also moves along its orbit around the Sun. Therefore, Earth must rotate a little more than one complete turn for the Sun to return to the zenith position, roughly an additional 1/365 of a full turn. This extra rotation takes approximately 4 minutes, meaning that a solar day is generally 24 hours long, on average.
It is important to note that there are slight variations in the actual length of the solar day throughout the year, but for practical timekeeping, we use the mean solar day, which is exactly 24 hours. This is the basis for our clocks and calendars, and it is this measure that is the answer to the student's question. Therefore, the correct answer to the question is (b) 24 hours.