Choose the odd one out from the following terms and name the category to which the others belong:
Dust, Smoke, Carbon monoxide, Effluents.
Topic: Air pollutants
Answer
Odd one out: EFFLUENTS. Category of the others: AIR POLLUTANTS.
Dust, smoke and carbon monoxide all pollute the AIR.
EFFLUENTS are liquid wastes discharged from factories into rivers and lakes — they pollute WATER.
So the division is by the MEDIUM polluted, not by whether the substance is harmful. Identifying the medium is the quickest way through odd-one-out questions in this chapter, since the syllabus divides pollution into air, water, soil, noise and radiation.
Note that dust and smoke are PARTICULATE pollutants (solid particles suspended in air) while carbon monoxide is a GASEOUS one — a real distinction, but not the one being asked, because it would separate two from two rather than three from one.