NH4+ and NH3 are an acid-conjugate base pair, since NH4+ is an acid, while NH3 is its conjugate base (since it is without the H+).
H2O and H3O+ can also be considered an acid-conjugate base pair, since H3O+ is an acid, while H2O would be its conjugate base. (But if only 1 answer is to be selected, it should be the NH4+ and NH3)
NH4+ and H3O+ are both acids, and both H2O and NH3 can be considered bases.
What is most widely accepted today is the giant-impact theory. It the Moon formed during a collision between the Earth and another small planet, about the There may indeed be several objects in orbit around Earth.
The rate at which radioactive decay occurs & how much radioactive decay has occurred
