Answer: The answer is D, Coal
hope this helps.
1/8=(1/2)^3 and the half life of radon is 3.8days
Half life is the time it takes for half of any amount of a radioactive substance to decay into something else.
Therefore for a sample of radon to decay to 1/8 of its original amount, it would take 3 x 3.8days=11.4 days
