Final answer:
The jovian planets are not primarily composed of hydrogen and helium.
Step-by-step explanation:
The statement is false. The jovian planets, which include Jupiter and Saturn, are primarily composed of hydrogen and helium. According to scientific observations and calculations, these two elements make up about 75% of the mass of Jupiter and Saturn. The remaining 25% is composed of other elements, such as trace amounts of methane and ammonia. Uranus and Neptune, on the other hand, consist in large part of compounds of carbon, nitrogen, and oxygen.