Arrhenius theorized that a base is a chemical compound that

Arrhenius theorized that a base is a chemical compound that contains hydroxide ions (OH⁻) and ionizes in water releasing them.

Explanation:

Svante Arrhenius was the first scientist to theorize about acids and bases.

Arrhenius' acid  base theory states that an acid is a compound that contains hydrogen atoms and ionizes in water to produce hydrogen ions (H⁺), and a base is a compound that contains hydroxide ions (OH⁻) that are released in water.

These are some examples of compounds which can be named as acid or base following Arrhenius' theory:

This theory is limited because it does not include compounds that do not contain or ionizes producting H⁺ or OH⁻. E.g. NH₃, which is a base (according to other theory).

h let me think

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.