Why is saturn almost as big as jupiter, despite its smaller mass?
a. saturn's rings make the planet look bigger. jupiter's strong magnetic field constrains its size.
b. saturn has a larger proportion of hydrogen and helium than jupiter, and is therefore less dense.
c. jupiter's greater mass compresses it more, thus increasing its density.
d. saturn is further from the sun, thus cooler, and therefore less compact.

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.

igneous rocks also form where plates converge. the subducting plate melts as it sinks into the crust of the earth, and the melt rises into the overriding plate forming volcanoes. metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. -woods