Another term for natural radioactive decay into another element is

The process of unstable (or radioactive) atoms becomes stable by emitting radiation. This event over time is called radioactive decay. Alpha decay results in the loss of two protons and two neutrons from the nucleus

radioactive disintegration

Explanation:

in chemistry, a solution’s concentration is how much of a dissolvable substance, known as a solute, is mixed with another substance, called the solvent. the standard formula is c = m/v, where c is the concentration, m is the mass of the solute dissolved, and v is the total volume

level 4 to level 2 : ))