The correct option is Hydration.
Explanation
Chemical weathering involves the decomposition of rocks and minerals through chemical reactions. These processes include solution, carbonation, hydration, oxidation, and reduction, which act on rocks to decompose, dissolve, or reduce them to a fine clastic state.
Detailed Analysis:
- Carbonation is incorrect: Carbonation is the reaction of carbonate and bicarbonate ions with minerals. It typically involves carbonic acid (formed by carbon dioxide dissolving in water) reacting with rocks like limestone and feldspars. It does not primarily involve expansion through water absorption.
- Oxidation is incorrect: Oxidation refers to the combination of a mineral with oxygen to form oxides or hydroxides. It occurs where there is ready access to the atmosphere and oxygenated waters (e.g., rusting of iron) and is not defined by water absorption.
- Hydration is correct: Hydration is the chemical addition of water. In this process, minerals take up water and expand; this expansion causes an increase in the volume of the material itself or the rock. This volume increase creates physical stress within the rock, leading to disintegration. A common example is calcium sulphate taking in water to turn into gypsum.
- Reduction is incorrect: Reduction occurs when oxidised minerals are placed in an environment where oxygen is absent, such as below the water table or in waterlogged ground. It involves the removal of oxygen rather than the absorption of water for expansion.
Key Takeaway: Hydration is the specific chemical weathering process where minerals absorb water, resulting in volume expansion and subsequent physical stress on the rock structure.