Which of the following is a chemical change involved in the formation of soils?

• A. Abrasion of rocks by wind
• B. Cracking of rocks due to plant root growth
• C. Breaking of rocks into smaller pieces by freezing and thawing
• D. Oxidation of iron minerals

Answer: (D)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: Physical changes alter the form or appearance of a substance without changing its chemical composition, while chemical changes result in the formation of new substances with different chemical properties.
2. Analyze each option to determine if it represents a physical or chemical change. For example, abrasion of rocks by wind, cracking due to root growth, and breaking by freezing and thawing are all physical processes because they change the rock's size or shape but not its chemical composition.
3. Recognize that oxidation of iron minerals involves a chemical reaction where iron reacts with oxygen (often from air or water) to form new compounds such as iron oxides (rust), which is a chemical change.
4. Recall that soil formation involves both physical weathering (breaking down rocks physically) and chemical weathering (altering the chemical composition of minerals), with oxidation being a key chemical weathering process.
5. Conclude that among the given options, oxidation of iron minerals is the chemical change involved in soil formation because it changes the chemical identity of the minerals.