Final answer:
The half-life of radioactive sodium (Na24) is 15 hours, which means it takes 15 hours for half of the Na24 to decay.
Step-by-step explanation:
The half-life of a radioactive isotope is the time required for half the atoms in a sample to undergo radioactive decay. In this case, the half-life of sodium-24 (Na24) is 15 hours. If a research assistant made 160 mg of radioactive Na24, after 15 hours, only 80 mg of Na24 would remain due to its half-life. The half-life is an important concept in understanding how radioactive materials decay over time and is used in calculations regarding radioactivity and nuclear medicine.