D

Step 1: Understand the concept of periodic time for a satellite. The periodic time, or orbital period, is the time it takes for a satellite to make one complete orbit around the Earth.

Step 2: For satellites in geostationary orbit, which is commonly used for communication satellites, the orbital period must match the Earth's rotation period to remain in a fixed position relative to the Earth’s surface. This is referred to as a geostationary satellite.

Step 3: The Earth rotates once every 24 hours. Therefore, a geostationary satellite must also have a periodic time of 24 hours, ensuring it remains in sync with the rotation of the Earth.

Conclusion: The correct periodic time for a communication satellite in a geostationary orbit is indeed 24 hours.
Therefore, the answer is D.