How many grams of cobalt-60 will remain after three half-lives?

Cobalt-60 decays, with a half-life of 5.3 years, to the element nickel-60 by the emission of a 0.32 MeV beta particle.

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.