Dobson Units (DU) are used to measure :

The correct answer is Option (2) → Thickness of ozone layer

Option (2) Thickness of ozone layer — Correct. The ozone in a column of air from the ground to the top of the atmosphere is measured in Dobson units.

Note 1: A similar question was also asked in CUET (UG) 2023 on 15-06-2023 (Slot 1).

Note 2: This question is from Chapter 16, Environmental Issues, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 16, Environmental Issues):
Ozone Depletion in the Stratosphere – “… There is ‘good’ ozone also; this ozone is found in the upper part of the atmosphere called the stratosphere, and it acts as a shield absorbing ultraviolet radiation from the sun. UV rays are highly injurious to living organisms since DNA and proteins of living organisms preferentially absorb UV rays, and its high energy breaks the chemical bonds within these molecules. The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).”