Passage II
When the nucleus of an atom of a radioactive isotope undergoes certain types of decay, the atom transforms into an atom of a different isotope. An isotope's half-life is the time it takes for half of any given number of its nuclei to decay. An isotope's decay constant, λ, depends on the isotope's rate of decay. Table 1 gives the value of λ (in 
) for 8 isotopes of different elements.
Figures 1 and 2 show, for each of 6 of the isotopes listed in Table 1, the change over time in the number of the nuclei remaining,
, in a sample initially containing 1,000 of the nuclei.
(Note: In Figure 1, the unit of time is years; in Figure 2, the unit of tine is days.)
11. Based n Figure 2, if a sample contained 2,000 atoms of Fe-59 at time = 0, at approximately what time will the of the sample be 400 ?
Your Answer is
Correct Answer is D
Explanation
The total number of 2000 decays to 400, which is equivalent to the total number of 1000 decaying to 200. According to figure 2, it can be seen that when the vertical coordinate is 200, the corresponding vertical coordinate of Fe-59 is about 100