QUES . Consider the following statements: UPSC 2024

Statement-I:

Rainfall is one of the reasons for weathering of rocks.

Statement-II:

Rain water contains carbon dioxide in solution.

Statement-III:

Rain water contains atmospheric oxygen.

Which one of the following is correct in respect of the above statements?

(a) Both Statement-II and Statement-III are correct and both of them explain Statement-I.

(b) Both Statement-II and Statement-III are correct, but only one of them explains Statement-I.

(c) Only one of the Statements II and III is correct and that explains Statement-I.

(d) Neither Statement-II nor Statement-III is correct.

Ans (a)

Must read: Weathering : Definition, Types and Significance

EXPLANATION:

Rainfall and temperature can affect the rate in which rocks weather. High temperatures and greater rainfall increase the rate of chemical weathering. Rocks in tropical regions exposed to abundant rainfall and hot temperatures weather much faster than similar rocks residing in cold, dry regions. Hence, Statement-I is correct.

Natural rain water is slightly acidic (pH = 5.6) since there is carbon dioxide in the atmosphere that dissolves to make carbonic acid. This acid reacts with minerals in the rocks. This type of weathering is important in the formation of caves. Hence, Statement-II is correct.

Generally, rainwater contains very low levels of dissolved oxygen because it absorbs oxygen from the atmosphere as it falls through the air. When oxygen combines with water and iron, it weakens the rock and breaks it. Example, oxidation of iron.Hence, Statement-III is correct.

Both Statement-II and Statement-III are correct and both of them explain Statement-I.