Hydrogen Ions — Common, right? The Wikipedia entry for Ion states "A positively charged hydrogen ion (or proton) can readily combine with other particles and therefore is only seen isolated when it is in a gaseous state or a nearly particle-free space." Cells pumping ions across membranes is very common so can someone help me understand what context might be implied by the quote?

I'm still not entirely sure what specifically you're asking about, but I have a guess. It is true that positively-charged hydrogen ions, or bare protons, are typically only observed in gaseous/plasma states and hard vacuums, and it is also true that cells routinely pump positively-charged hydrogen ions across membranes. This is not a paradox because in aqueous solutions, hydrogen ions exist as $H_3O^+$, also known as hydronium or hydroxonium.

![Hydronium](

Image from Wikimedia Commons