When two or more different kinds of atoms join together, they form a:
1.compound
2.mixture
3.union

1. compound

Explanation:

Compound because these atoms connected by chemical bonds.

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.