Question

Assertion :The primitive atmosphere was reducing one i.e., without oxygen. Reason: In the primitive atmosphere, oxygen was involved in forming ozone layer.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

Answer: (C)

• The lightest atoms of nitrogen, carbon, etc, formed the primitive atmosphere. Hydrogen atoms were most reactive in the primitive atmosphere so, they combined with all oxygen atoms to form water leaving no free oxygen.
• Thus, the primitive atmosphere was reducing atmosphere (without free oxygen) unlike the present oxidizing atmosphere (with free oxygen).
• The formation of the ozone layer is the consequence of the modern oxidizing atmosphere having plenty of free oxygen. As more oxygen accumulated in the atmosphere (due to photosynthesis) ozone began to appear in the top layers.

Thus, the correct answer is option C.