How are the concentrations of hydrogen ions and hydroxide ions related in an aqueous solution?

An Arrhenius acid increases the concentration of hydrogen (H+) ions in an aqueous solution, while an Arrhenius base increases the concentration of hydroxide (OH–) ions in an aqueous solution.

An Arrhenius acid increases the concentration of hydrogen (H+) ions in an aqueous solution, and

Arrhenius base increases the concentration of hydroxide (OH–) ions in an aqueous solution.

radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

dynamic equilibrium is the answer.