Based on mass, the number of earth that could fit inside Jupiter

as already noted, Jupiter is more massive than all the other planets in our Solar System – 2.5 times as massive, that is. In fact, Jupiter weighs in at a hefty 1.8986 × 1027 kg (~4.1857 x 1027 lbs), or 1898.6 billion trillion metric tons (2.092 billion trillion US tons).

Compare that to Earth

b. the carbon cycle ensures living things have a source of hydrogen

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.