Which is a cause of physical weathering? A. acid rain B. carbon dioxide C. erosion D. water

The correct answer is: **D. water** **Explanation:** **Physical weathering** refers to the mechanical breakdown of rocks and minerals into smaller pieces without changing their chemical composition. Water plays a significant role in physical weathering through several processes: 1. **Freeze-Thaw Cycles (Frost Wedging):** - Water seeps into cracks in rocks. - When temperatures drop below freezing, the water freezes and expands. - The expansion exerts pressure on the surrounding rock, causing it to crack and eventually break apart. 2. **Abrasion:** - Flowing water can carry sediments that scrape against rock surfaces. - This constant grinding can wear down and smooth the rocks over time. 3. **Thermal Expansion:** - While more associated with temperature changes, water can aid in this process by facilitating heat transfer, leading to the expansion and contraction of rock materials. **Why the Other Options Are Not Correct:** - **A. Acid Rain:** This is primarily a **chemical weathering** process. Acid rain contains dissolved acids that react with minerals in rocks, leading to chemical changes and breakdown. - **B. Carbon Dioxide:** While CO₂ can contribute to both chemical weathering (by forming carbonic acid) and physical processes indirectly, on its own, it is more directly linked to chemical weathering rather than physical weathering. - **C. Erosion:** Erosion is the **removal and transportation** of weathered materials by natural agents like water, wind, or ice. It is separate from the weathering process itself, which involves the breakdown of rocks in place. **Summary:** Water is a key agent in physical weathering through its ability to cause mechanical breakdown of rocks via processes like freeze-thaw cycles and abrasion.