Final answer:
The approximate radius of a hydrogen/helium planet with a mass one-tenth that of Jupiter would be about 0.9 times the radius of Jupiter.
Step-by-step explanation:
The approximate radius of a hydrogen/helium planet with a mass one-tenth that of Jupiter can be determined using models of planetary mass and radius for gas giants. Despite having a significantly lower mass, such planets do not shrink in radius proportionally due to the way gas behaves under compression. The radius would be less affected by the reduction in mass. Therefore, the answer is b.about 0.9 times the radius of Jupiter. This is because the relationship between mass and radius for gas giants is not linear and a more massive planet like Jupiter does not have a radius 10 times that of a planet 1/10th its mass, mainly due to the physics of degenerate matter in such dense planetary interiors.