Answer:
c. Jupiter's greater mass compresses it more, thus increasing its density.
Explanation:
The mass of Jupiter is greater in its interior, this mass compresses Jupiter to some extent. Thus, its density is increased. Now, more mass is compressed in the lesser volume. Hence, its size does not increase enormously. On the other hand the mass of Saturn is lesser and also density lower. this gives Saturn a reasonably higher volume.
Hence, option C is correct.