When radon-220 nucleus emits a gamma ray, what nucleus remains?

Gamma ray is an energy emission. In Gamma decay there is no any particle decay from the parent nucleus. It is just an unstable nucleus becomes as stable by releasing energy as photon. That energy releases as a gamma ray. Hence, there is no change in atomic number or mass number of the daughter atom.

Hence, radon (Rn) remains as same after undergoing a gamma decay but in less energy.

answer; i do believe the correct answer is (river); /// good luck

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.