[poll id=”150″]
ANSWER: B. 43.75g
This is a type of problem that can be seen in either general chemistry or the physics section, but it is EXPECTED to be on the OAT. Not knowing how to answer these simple (but mandatory) problems will lose you vital points in your OAT. After 12 days, the element will have undergone a “half-life” of 3 cycles, as each half life period is 4 days. Thus: 50g -> 25g (1 half life / 4 days)
25g -> 12.5g (2 half life / 8 days)
12.5g -> 6.25g (3 half life / 12 days)
Thus by 12 days, 6.25g of the element remains. However, since the question asks for the amount that has decayed, simply subtract the original mass with the remaining mass: 50g – 6.25g = 43.75g