Final answer:
The angular momentum of an orbiting planet is equal at both aphelion and perihelion due to the conservation of angular momentum. At aphelion, the planet has a greater moment of inertia but moves slower, while at perihelion it has a smaller moment of inertia but moves faster.
Step-by-step explanation:
The question is related to the comparison of the angular momentum of a planet at two different points in its orbit around the sun: aphelion and perihelion. Based on the principles of physics, particularly conservation of angular momentum, the angular momentum of a planet in orbit remains constant provided there is no external torque. This means at aphelion, where the planet is farthest from the sun, it has greater moment of inertia but moves more slowly. Conversely, at perihelion, where the planet is closest to the sun, it has a smaller moment of inertia but moves faster. As a result, the angular momentum at both points is equal (option c).
Comparing the angular momentum of a planet at aphelion or perihelion with that of the Moon rotating on its axis is not directly related, as the question concerns the Moon keeping one face towards Earth due to tidal locking, which involves torques and energy dissipation, unlike an orbiting planet where no external torque is considered.