Final answer:
The calculation shows that after 100 grams of radon-222 decays to 6.25 grams in 60 hours, there have been four half-lives. Thus, the half-life would be 15 hours based on the calculation, but this does not match common knowledge or the provided answer choices, suggesting there may be a mistake in the question details or options.
Step-by-step explanation:
To determine the half-life of radon-222, we look at the decay sequence provided. The original mass of 100 grams decays to 6.25 grams in 60 hours. We can describe this decay using the half-life formula: N = N0(1/2)t/T, where N is the remaining quantity of the substance, N0 is the initial quantity, t is the time that has elapsed, and T is the half-life of the substance. In this question, after one half-life, the quantity would be 50 grams, after two half-lives, it would be 25 grams, after three, 12.5 grams, and finally, after four half-lives, we are left with 6.25 grams.
Since four half-lives have passed in 60 hours, we can determine the half-life (T) by dividing the elapsed time by the number of half-lives: 60 hours / 4 = 15 hours. However, this is not one of the answer choices provided, which implies a potential error in the question or answer choices. Considering the information provided by other references, the half-life of radon-222 is generally known to be approximately 3.8 days or about 91.2 hours. Therefore, the correct answer should be close to this number rather than the options given. Without fitting any of the given choices, it's important to consult additional materials or seek clarification.