Final answer:
Kepler's laws are valid in inertial frames and are purely descriptive. They provide geometric descriptions of planetary motion but do not explain the forces causing these motions.
Step-by-step explanation:
Kepler's laws of planetary motion are valid in inertial frames of reference. These laws offer a precise geometric description of the movements of planets within the Copernican system, which was a heliocentric model placing the Sun at the center of the universe. Kepler's laws enabled highly accurate calculations of planetary positions. While providing this descriptive clarity, Kepler's laws are purely descriptive; they do not explain the underlying causes or forces behind the motions of the planets. This aspect—the understanding of the forces involved—was later addressed by Isaac Newton with his law of universal gravitation.
The answer to the question, 'In what frame(s) of reference are Kepler’s laws valid? Are Kepler’s laws purely descriptive, or do they contain causal information?' is (d) Inertial frames; contain descriptive information. Even though the laws describe how planets move, they do not provide the causal explanation, which is why it is said they contain descriptive information, not causal.