Which of the following is not a process of chemical weathering?

The correct answer is Exfoliation.

Key Points

Chemical weathering:

• Chemical weathering is the process of chemical decomposition of rocks and soil.
• Chemical weathering involves the rock interacting with chemicals to alter the rock's composition.
• A cluster of weathering processes namely solution, carbonation, hydration, oxidation, and reduction. 
• These processes act on rocks to decompose, dissolve or moderate them to a fine clastic state through chemical reactions by oxygen, surface/ soil water, and other acids.
• Water and air along with heat must be present to speed up all chemical reactions.

Additional Information

Exfoliation:

• Over time, sheets of rock break away from the exposed rocks along the fractures, a process known as exfoliation. Hence, option 4 is correct.
• Exfoliation due to pressure release is also known as “sheeting“.
• Temperature changes can also contribute to mechanical weathering in a process called thermal stress.
• The surface layers of the rocks tend to expand more than the rock at depth, and this leads to the peeling off of the surface layers (exfoliation).