Final answer:
The most common element in Jovian planets is hydrogen, making up about 75% of the mass of Jupiter and Saturn, which results in them also being known as 'liquid planets' due to the liquefied state of hydrogen caused by extreme pressure.
Step-by-step explanation:
The most common element found in Jovian planets, also known as the gas giants, is hydrogen. Jupiter and Saturn, which are the largest of the Jovian planets, have a chemical composition similar to that of the Sun, consisting primarily of hydrogen and helium.
Approximately 75% of their mass is hydrogen, while helium makes up about 25%. It is important to note that despite being commonly referred to as gas planets, the intense pressure within these planets compresses the hydrogen into a liquid state.
Therefore, they could also be referred to as 'liquid planets' due to the state of the majority of their mass. On the other hand, Uranus and Neptune also have hydrogen in their atmospheres but consist largely of compounds formed from elements like oxygen, carbon, and nitrogen.