It is B, <span>In fact, water will sink as it cools until a certain point. If I recall correctly this is around 39 F. As the temp gets lower than that water actually begins to expand and becomes less dense. This is why ice floats, which we should all be thankful for. If ice didn't float than all water on earth would likely freeze solid and life would have probably never evolved past small single celled things.</span>
Communism is the correct answer
Set this up as
10 = 40 (1/2)t/28
and solve for t in years.
10/40 = (1/2)t/28
log(0.25) = (t/28) log(0.5)
t = 28 log(0.25) / log(0.5) years = 56 years
Test the answer:
56 years = 2(28 years) = 2 half-lives, so the remaining amount should be 1/2 of 1/2 of the initial amount, i.e. 1/4 of the initial amount, and 10 mg = 1/4 of 40 mg.
