# Is most hydrogen in the universe in the form of plasma, atomic neutral hydrogen, ionized hydrogen, or molecular?

Some places say most hydrogen is plasma, such as the stuff stars are made of (mostly) and the 'warm-hot intergalactic plasma'.

Other places say neutral atomic hydrogen (H(I) to astronomers), such as the stuff in the interstellar medium, is the most common...

• It would be better if you added at least one example for each of "Some places say..." and "Other places say..." Thanks!
– uhoh
Sep 12 '20 at 4:31
• Molecular hydrogen is known as H$_2$. "H III" would suggest hydrogen that has lost two electrons, except that since hydrogen only has one electron, there would be no such ion. Sep 12 '20 at 19:00

According to Wikipedia, most Hydrogen is in the form of Atomic and Plasma states.

Throughout the universe, hydrogen is mostly found in the atomic and plasma states, with properties quite distinct from those of molecular hydrogen.

Intuition says that because, as this link says, 99.9% matter in the universe is plasma, most Hydrogen in the universe should also be present in Plasma state.

"99.9 percent of the Universe is made up of plasma," says Dr. Dennis Gallagher, a plasma physicist at NASA's Marshall Space Flight Center. "Very little material in space is made of rock like the Earth."

This link has the calculations to determine the amount of Hydrogen in Plasma in relation to the total amount of Plasma (if anyone is interested...)

Stars are made of relatively simple stuff. By mass, our Sun is 73% hydrogen, 26% helium, and only 1% of higher Z (atomic number) atoms.

X = mHnH / r = density of hydrogen / total density

Though I am not sure about the actual answer about the same, I will be grateful if anyone can point out to the right answer. And although I have made every effort into the removal and rectification of errors, If there are any errors in my answer, I will be grateful if anyone can point them out.

• Cam anyone please confirm if my answer is correct? Sep 14 '20 at 5:39