Online Test — Environmental Chemistry
20 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 20
The protective ozone layer that absorbs UV radiation lies in the:
troposphere
stratosphere
mesosphere
exosphere
Explanation: Ozone (O3) is concentrated in the stratosphere, where it absorbs harmful UV-B radiation.
Question 2 of 20
Carbon monoxide is poisonous because it:
forms acid rain
depletes ozone
causes eutrophication
binds haemoglobin more strongly than oxygen
Explanation: CO forms stable carboxyhaemoglobin, blocking oxygen transport in the blood.
Question 3 of 20
Acid rain mainly contains:
H2SO4 and HNO3
HCl and HF
H2CO3 only
NaOH and KOH
Explanation: SO2 and NO2 dissolve in rain to form sulphuric and nitric acids.
Question 4 of 20
Photochemical smog is an example of:
a reducing smog
harmless fog
stratospheric pollution
an oxidising smog
Explanation: It contains oxidants like ozone and PAN, formed from NO2 and hydrocarbons in sunlight.
Question 5 of 20
The catalytic species that destroys stratospheric ozone is:
CO2
SO3
Cl• (chlorine radical)
CH4
Explanation: Chlorine radicals from CFCs destroy ozone repeatedly: Cl• + O3 → ClO• + O2.
Question 6 of 20
Which gas is NOT a greenhouse gas?
CO2
CH4
N2
Water vapour
Explanation: Diatomic N2 does not absorb infrared radiation and is not a greenhouse gas.
Question 7 of 20
A high BOD value in water indicates:
clean water
high dissolved oxygen
heavy organic pollution
absence of microbes
Explanation: Higher BOD means more organic matter and greater oxygen demand, i.e. more pollution.
Question 8 of 20
Eutrophication of lakes is caused mainly by excess:
nitrates and phosphates
dissolved oxygen
chloride ions
noble gases
Explanation: Nitrate/phosphate run-off triggers algal blooms whose decay depletes oxygen.
Question 9 of 20
DDT is classified as a/an:
herbicide
insecticide
fungicide
fertiliser
Explanation: DDT is a persistent insecticide that biomagnifies up the food chain.
Question 10 of 20
Dissolved oxygen in clean natural water is about:
8 to 10 mg/L
0 mg/L
50 mg/L
200 mg/L
Explanation: Clean water holds roughly 8–10 mg of dissolved O2 per litre.
Question 11 of 20
Green chemistry primarily aims to:
treat waste after release
prevent pollution at source by design
increase chlorine use
raise reaction temperatures
Explanation: It designs processes that avoid generating hazardous substances in the first place.
Question 12 of 20
A reaction is greener when its atom economy is:
lower
negative
higher
zero
Explanation: High atom economy means more reactant atoms end up in the product and less waste forms.
Question 13 of 20
Hydrogen peroxide bleaching is green because H2O2 decomposes to:
chlorine and acid
water and oxygen
CO2 and soot
ozone and PAN
Explanation: 2H2O2 → 2H2O + O2, leaving harmless by-products.
Question 14 of 20
Liquefied CO2 in green dry cleaning replaces the harmful solvent:
water
tetrachloroethene (PERC)
hydrogen peroxide
ethanol
Explanation: PERC is a suspected carcinogen; liquid CO2 is a safe, reusable alternative.
Question 15 of 20
Which oxide is mainly responsible for the brown colour of photochemical smog and its formation?
CO
NO2
CO2
SO3
Explanation: NO2 is brown and, with hydrocarbons in sunlight, drives photochemical smog.
Question 16 of 20
Excess UV-B radiation reaching the Earth due to ozone depletion can cause:
skin cancer and cataracts
more rainfall
higher oxygen levels
global cooling
Explanation: UV-B damages DNA, increasing skin cancer and eye cataracts and harming crops.
Question 17 of 20
Match the pollutant to its source: SO2 comes mainly from:
burning sulphur-containing fossil fuels
fertiliser run-off
algal blooms
CFC sprays
Explanation: Burning coal and other sulphur-rich fuels releases SO2.
Question 18 of 20
Biogas obtained by digesting biodegradable waste is mainly:
nitrogen
methane
chlorine
sulphur dioxide
Explanation: Anaerobic digestion of organic waste produces methane-rich biogas.
Question 19 of 20
The natural pH below which rain is considered 'acid rain' is about:
5.6
7.0
8.5
9.2
Explanation: Unpolluted rain is slightly acidic (~5.6 from dissolved CO2); below this it is acid rain.
Question 20 of 20
Which compound is used as a fungicide and can release toxic mercury into soil?
sodium chlorate
DDT
organomercury compound
ammonium nitrate
Explanation: Organomercury compounds are fungicides that can leave toxic mercury residues.