Contains several large elliptical galaxies. A small cluster containing a few dozen members. A rich cluster with thousands of galaxies. Hydrogen is ionized in hot stars. Hot stars are made mostly of helium.
Most hydrogen is in molecular form in hot stars.
Destroying the ozone layer. Increasing the frequency with which El Nino occurs. The Universe has positive curvature and will eventually collapse on itself. The Universe has positive curvature and will never collapse on itself. The Universe has negative curvature and will eventually collapse on itself.