Which of the following are examples of organic pollutants in water? A. Salts…
2024
Which of the following are examples of organic pollutants in water?
A. Salts
B. Pesticides
C. Dioxins
D. Bases
E. Pigments
Choose the correct answer from the options given below:
Answer: D. B, C and E only — ConceptWater pollutants are classified by the chemical nature of the polluting substance. An organic pollutant is a carbon-based compound: its molecule is…
- A.
A, B and C only
- B.
B, C and D only
- C.
C, D and E only
- D.
B, C and E only
Show answer & explanation
Correct answer: D
Concept
Water pollutants are classified by the chemical nature of the polluting substance. An organic pollutant is a carbon-based compound: its molecule is built on a skeleton of carbon atoms bonded to hydrogen, oxygen, chlorine or nitrogen, and it is either produced by living matter or synthesised from petrochemical feedstock. An inorganic pollutant has no such carbon skeleton — acids, alkalis, mineral salts and heavy-metal ions are the standard inorganic examples. So the test for each listed substance is simply: does a carbon skeleton define the molecule?
Applying the test to each listed substance
Listed substance | What the substance is | Class |
|---|---|---|
A. Salts | Ionic compounds of a metal with an acid radical — sodium chloride, sulphates, nitrates; they raise salinity and TDS | Inorganic |
B. Pesticides | Synthetic carbon-chain molecules such as DDT, endosulfan and organophosphates, reaching water bodies as farm run-off | Organic |
C. Dioxins | Chlorinated benzene-ring compounds released by waste incineration and pulp bleaching; listed as Persistent Organic Pollutants (POPs) | Organic |
D. Bases | Alkalis such as sodium hydroxide (NaOH) and lime discharged in industrial effluent; they push up the pH | Inorganic |
E. Pigments | Azo and anthraquinone dye molecules discharged by textile, dyeing and printing units | Organic |
Salts and bases are mineral species — an acid radical bound to a metal, or a metal hydroxide — so no carbon skeleton is involved and both belong to the inorganic group. Pesticides, dioxins and pigments are all built on carbon chains or benzene rings, which places all three in the organic group.
Cross-check with an independent test
The same classification can be reached from the laboratory side, without looking at a single structural formula. The standard analytical measure of the organic content of a water sample is Total Organic Carbon (TOC): the sample is oxidised and the carbon dioxide released from the carbon skeletons of its dissolved and suspended matter is measured, while carbonate and bicarbonate carbon is stripped out beforehand and reported separately as inorganic carbon. TOC is an aggregate, class-level measure and does not identify individual compounds, but it tests exactly the property this question turns on: a substance can contribute to it only if a carbon skeleton is there to be oxidised. Pesticide residues, dioxins and dye pigments belong to the class the TOC channel responds to, whereas dissolved chlorides, sulphates, nitrates and hydroxides cannot contribute to it at any concentration and register only in conductivity, TDS and pH. The analytical split therefore falls in the same place as the definitional one. Applying that to the groupings offered, only the grouping made up of pesticides, dioxins and pigments contains no mineral species; every other grouping places salts or bases in the organic class, which the definition rules out. Hence the organic examples in the list are pesticides, dioxins and pigments, i.e. the combination B, C and E only.