Identify the correct sequence of processes involved in chemical weathering of rocks.
(A) Carbonation
(B) Solution
(C) Hydration
(D) Oxidation
(E) Reduction
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B), (A), (C), (D), (E)
Chemical weathering is the breaking down of rocks by chemical reactions with water, air and the substances dissolved in them, which change the minerals of the rock. Its processes, in this order, are: solution, carbonation, hydration, oxidation and reduction.
(B) Solution — minerals such as rock salt and gypsum dissolve in water and are carried away.
(A) Carbonation — carbon dioxide dissolved in rainwater forms a weak carbonic acid that dissolves limestone and other calcium carbonate rocks.
(C) Hydration — minerals take up water and swell, which strains the rock until it crumbles.
(D) Oxidation — minerals, mostly iron compounds, combine with oxygen, giving the red-brown colour of rusted rock.
(E) Reduction — where oxygen is scarce, as below the water table, oxygen is removed from the minerals.
Note: It seems that there is a mistake in the original NTA question: the processes of chemical weathering do not take place one after another in a fixed sequence, and they often act on a rock at the same time. Option (1) is the order in which the textbook lists and describes them, so it is the most appropriate answer.