Need help with this chemistry problem

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.

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.