Which of the following are process of physical weathering? I. Frost action II. Hydrolysis III. Oxidation IV. Temperature Changes

Step 1: Analyze the question You are asked to pick the processes that are physical (mechanical) weathering. These break rock into smaller pieces without changing its chemical composition.

Step 2: Key concept

• Physical weathering: Rocks break down by physical forces. Examples are frost action (freeze-thaw), temperature changes (expansion and contraction, which cause exfoliation), pressure release, and salt crystallization.
• Chemical weathering: The minerals in the rock change chemically. Examples are hydrolysis, oxidation, carbonation, hydration and solution.

Step 3: Classify each process

• I. Frost action: Physical. Water enters cracks, freezes, expands and wedges the rock apart.
• II. Hydrolysis: Chemical. Water reacts with minerals such as feldspar and turns them into clay.
• III. Oxidation: Chemical. Oxygen reacts with iron minerals and forms rust-coloured compounds.
• IV. Temperature changes: Physical. Repeated heating by day and cooling by night makes the rock expand and contract until it cracks or peels. This is common in hot desert and savanna areas in northern Nigeria.

Step 4: Match to the options Physical weathering = I and IV.

• A (I and III): III is chemical, so it is wrong.
• B (I and IV): correct.
• C (III and IV): III is chemical, so it is wrong.
• D (II and III): both are chemical, so it is wrong.

Tip: Think "H-O-C-S" for chemical weathering: Hydrolysis, Oxidation, Carbonation, Solution. Anything with water reacting or oxygen reacting is chemical. Anything involving freezing, heating, cooling or cracking is physical.