The effective half-life of an injected radionuclide depends on which two factors?

The effective half-life of an injected radionuclide is the time it takes for the radioactivity of the substance in the body to decrease to half its initial value, taking into account both the physical decay of the radionuclide and its biological elimination from the body. The two key factors that determine the effective half-life are its radioactive half-life and biological half-life.

The radioactive half-life is the time required for the radionuclide to decay to half of its original radioactivity due to its inherent physical properties. This decay process occurs regardless of biological factors. The biological half-life, on the other hand, is the time it takes for the body to eliminate half of the substance through processes such as metabolism or excretion.

The effective half-life is calculated using both these half-lives because they both contribute to the total rate at which the radionuclide is eliminated from the body. By combining these two half-lives, one can find out how effectively the radionuclide is reduced in concentration in a living organism.

Thus, the effective half-life is dependent on both the biological half-life and the radioactive half-life, making the selected answer accurate and relevant in understanding how radionuclides behave within biological systems.