Answer:
To answer this question, we need to know the half-life of radon-222. Let's assume it has a half-life of 3.8 days.
If the initial amount of radon-222 is 100 grams, then after one half-life (3.8 days), it will have decayed to 50 grams. After two half-lives (7.6 days), it will have decayed to 25 grams.
Therefore, it will take 7.6 days for the amount of radon-222 to be reduced to 25 grams.