In which of the following units is thickness of ozone layer measured?

The correct answer is Option (1) → Dobson

Option (1) Dobson — Correct. The ozone over a place is measured in Dobson units (DU). A low reading marks thinning of the layer, as in the ozone hole.

Option (2) Joule — Incorrect. The joule is the unit of energy. It is used, for example, for the energy passed along a food chain.

Option (3) Newton — Incorrect. The newton is the unit of force, not of a gas layer.

Option (4) Decibel — Incorrect. The decibel (dB) measures the loudness of sound. It is the unit used for noise pollution.

Note: 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 Strato- – “… You have earlier studied in the Chemistry textbook of Class XI about ‘bad’ ozone, formed in the lower atmosphere (troposphere) that harms plants and animals. 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).”