All natural and artificial radioactive decay of unstable nuclei take place by

First order kinetics

The correct answer is Option (2) → First order kinetics
All natural and artificial radioactive decay of unstable nuclei follows first order kinetics.
In radioactive decay, the rate of disintegration at any moment depends only on the number of undecayed nuclei present, not on concentration of any other substance.

This matches the definition of first order reaction, where:

• Rate ∝ Number of nuclei remaining

• Half-life is constant and independent of initial amount

Hence, radioactive decay always obeys first order kinetics.