The correct answer is option 2: Salt crystal growth.

Chemical weathering is the process by which rocks and minerals are broken down and altered through chemical reactions. In this case, salt crystal growth is not considered a type of chemical weathering.

1. Carbonation solution: This refers to the process where carbon dioxide in rainwater or moist air reacts with minerals like limestone to form carbonic acid. This acid then dissolves the minerals, causing weathering.

2. Salt crystal growth: This option is incorrect. Although salt crystal growth can contribute to the physical breakdown of rocks, it is not considered a type of chemical weathering.

3. Hydrolysis: Hydrolysis is a chemical weathering process that occurs when water reacts with minerals to produce new compounds. This reaction can break down minerals and weaken rocks.

4. Oxidation: Oxidation is a type of chemical weathering that involves the reaction of minerals with oxygen. This reaction can result in the breakdown of minerals and the alteration of rocks.

It`s important to remember that while salt crystal growth can physically break down rocks through the expansion and contraction of salt crystals, it is not considered a chemical weathering process.