Question 44

Oxygen reacts with iron in rocks to form rust.

This scenario illustrates chemical weathering, where a chemical reaction occurs between oxygen and iron in the rocks, resulting in the formation of rust.

A) Oxygen reacts with iron in rocks to form rust.

This option accurately represents chemical weathering as it involves a chemical reaction between oxygen and iron, which alters the mineral composition of the rock. This process leads to the breakdown of the rock structure, demonstrating the core principle of chemical weathering.

B) Blown sand grinds down exposed rocks in a desert.

This scenario describes physical weathering, specifically abrasion, where mechanical forces act on the rocks without changing their chemical composition. While it does lead to rock breakdown, it does not involve any chemical alteration, thus it is not an example of chemical weathering.

C) Tree roots crack rocks as they grow into cracks.

This option depicts physical weathering through biological means, where the growth of tree roots exerts pressure on the rocks, causing them to fracture. Although it contributes to rock disintegration, it does not involve any chemical processes, therefore it is not a demonstration of chemical weathering.

D) Cycles of hot and cold temperature form cracks in rocks.

This choice illustrates physical weathering due to thermal expansion and contraction, which leads to the cracking of rocks. Similar to the previous options, this process does not involve any chemical reaction or alteration, thus it is not related to chemical weathering.

Conclusion

The correct answer, which describes oxygen reacting with iron to form rust, is a clear example of chemical weathering due to the alteration of the rock's mineral composition. In contrast, all other options illustrate physical weathering processes that do not involve chemical changes in the rocks. Therefore, they fail to demonstrate the concept of chemical weathering being tested.