1. the half life of radon-222 is about 3.5 days. if a building ventilation system broke and there was an accumulation of 10 kg of radon gas. how much will radon will remain after 7 days?

2. workers at the at the nuclear facility have been injured by plutonium-239 and radioactive iodine-131, but its been 50 years since the plant has been closed and the nuclear waste there is stored underground in barrels. is the site dangerous? why?