Jai was measuring the radioactivity of different radioactive isotopes. Isotope A had a starting radioactive level of 50 g, and after 4 days it measured at 30 g. Isotope B had a starting radioactive level of 75 g, and after 4 days it measured at 25 g. Which best explains the isotopes?
Answer
A
Isotope A has a shorter half-life than Isotope B.
B
Isotope A has a longer half-life than Isotope B.
C
Isotope A has half the half-life of Isotope B.
D
Isotope A has twice the half-life of Isotope B.
Explanation
After 4 days, Isotope A retained 30/50 = 60% of its starting amount, while Isotope B retained 25/75 = 1/3. Since A lost a smaller fraction in the same time, it decays more slowly and has a longer half-life than B. The best choice is “Isotope A has a longer half-life than Isotope B.”
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