aluminium is a fairly reactive metal that often has a protective layer on due to oxidation
with air. this means it sometimes seems reluctant to react. name the protective layer.

passivation layer

Explanation:

The oxide layer that forms ontop of many metals is called the passivation layer.

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.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.