JEE Previous Year Questions (2021-23): Environmental Chemistry PDF Download

Q.1. Which of the following is true about freons?   [JEE Main 2023]
(a) These are radicals of chlorine and chlorine monoxide
(b) These are chemicals causing skin cancer
(c) These are chlorofluorocarbon compounds
(d) All radicals are called freons

Ans. c
Freons → chlorofluorocarbon compounds

Q.2. Given below are two statements: [JEE Main 2022]
Statement I : In polluted water values of both dissolved oxygen and BOD are very low.
Statement II : Eutrophication results in decrease in the amount of dissolved oxygen.
In the light of the above statements, choose the most appropriate answer from the options given below :
(a) Both Statement I and Statement II are true
(b) Both Statement I and Statement II are false
(c) Statement I is true but Statement II is false
(d) Statement I is false but Statement II is true

Ans. d
Since eutrophication is result of excessive growth of weed in water bodies, which consume dissolved oxygen of water bodies.
∴ Eutrophication decreases amount of dissolved oxygen in water bodies.
Polluted water has low value of dissolved oxygen, but high valueof BOD (Biological oxygen demand), since chemical and organic matter requires dissolved oxygen to get decompose.

Q.3. The photochemical smog does not generally contain: [JEE Main 2022]
(a) NO
(b) NO₂
(c) SO₂
(d) HCHO

Ans. c
Photochemical smog contain:
Ozone, nitric oxide, organic compounds, nitrogen dioxide, formaldehyde.
∴ SO₂ is not the part of photochemical smog.

Q.4. Some gases are responsible for heating of atmosphere (green house effect). Identify from the following the gaseous species which does not cause it. [JEE Main 2022]
(a) CH₄
(b) O₃
(c) H₂O
(d) N₂

Ans. d
Among the given gases, the green house gases which are responsible for heating the atmosphere are CH4, water vapour and ozone. Nitrogen is not a green house gas.

Q.5. The eutrophication of water body results in : [JEE Main 2022]
(a) loss of Biodiversity.
(b) breakdown of organic matter.
(c) increase in biodiversity.
(d) decrease in BOD.

Ans. a
Eutrophication is the process in which nutrient enriched water bodies support a dense plant population, which kills animal life by depriving it of oxygen and results in subsequent loss of biodiversity.

Q.6. Given below are two statements : One is labelled as Assertion A and the other is labelled as Reason R. [JEE Main 2022]
Assertion A : Polluted water may have a value of BOD of the order of 17 ppm.
Reason R : BOD is a measure of oxygen required to oxidise both the bio-degradable an non-biodegradable organic material in water.
In the light of the above statements, choose the most appropriate answer from the options given below.
(a) Both A and R are correct and R is the correct explanation of A.
(b) Both A and R are correct but R is NOT the correct explanation of A.
(c) A is correct but R is not correct.
(d) A is not correct but R is correct.

Ans. c
Highly polluted water could have a BOD value of 17 ppm or more.
The amount of oxygen required by bacteria to break down the organic matter present in a certain volume of a sample of water is called Biochemical Oxygen demand (BOD).
Hence A is correct but R is not correct.

Q.7. The measured BOD values for four different water samples (A-D) are as follows: A = 3 ppm; B = 18 ppm; C = 21 ppm; D = 4 ppm. The water samples which can be called as highly polluted with organic wastes, are [JEE Main 2022]
(a) A and B
(b) A and D
(c) B and C
(d) B and D

Ans. c
Highly polluted water should have BOD value of 17 ppm or more

Q.8. Polar stratospheric clouds facilitate the formation of : [JEE Main 2022]
(a) ClONO₂
(a) HOCl
(a) ClO
(a) CH₄

Ans. b

Q.9. Given below are two Statements: [JEE Main 2022]
Statement I : Classical smog occurs in cool humid climate. It is a reducing mixture of smoke, fog and sulphur dioxide.
Statement II : Photochemical smog has components, ozone, nitric oxide, acrolein, formaldehyde, PAN etc.
In the light of the above statements, choose the most appropriate answer from the options given below.
(a) Both Statement I and Statement II are correct.
(b) Both Statement I and Statement II are incorrect.
(c) Statement I is correct but Statement II is incorrect.
(d) Statement I is incorrect but Statement II is correct.

Ans. a

Q.10. On the surface of polar stratospheric clouds, hydrolysis of chlorine nitrite gives A and B while its reaction with its reaction with HCl produces B and C. A, B and C are, respectively
[JEE Main 2022]
(a) HOCl, HNO₃, Cl₂
(b) Cl₂, HNO₃, HOCl
(c) HClO₂, HNO₂, HOCl
(d) HOCl, HNO₂, Cl₂O

Ans. a
On the surface of polar stratospheric clouds, hydrolysis of chlorine nitrate as

Hence A, B and C are HOCl, HNO₃ and Cl₂ respectively. 

Q.11. Correct statement about photo-chemical smog is : [JEE Main 2022]
(a) It occurs in humid climate.
(b) It is a mixture of smoke, fog and SO₂.
(c) It is reducing smog.
(d) It results from reaction of unsaturated hydrocarbons.

Ans. d
Photochemical smog occurs in warm, dry and sunny climate. The main components of photochemical smog result from the action of unsaturated hydrocarbons and nitrogen oxides. This is an oxidising smog.

Q.12. The acid that is believed to be mainly responsible for the damage of Taj Mahal is
(a) sulfuric acid. [JEE Main 2022]
(b) hydrofluoric acid.
(c) phosphoric acid.
(d) hydrochloric acid.

Ans. a
CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂
Industries like oil refinery releases SO₂ which causes air pollution. It reacts with water to form acid rain when SO₂ mix with water it forms H₂SO₄ (Sulphuric acid). 

Q.13. Water sample is called cleanest on the basis of which one of the BOD values given below: [JEE Main 2021]
(a) 11 ppm
(b) 15 ppm
(c) 3 ppm
(d) 21 ppm

Ans. c
BOD is the biological oxygen demand. Cleanest water sample will have BOD value equal to 3 ppm as clean water could have BOD value of less than 5 ppm whereas highly polluted water could have BOD value of 17 ppm or more.

Q.14. BOD values (in ppm) for clean water (A) and polluted water (B) are expected respectively : [JEE Main 2021]
(a) A > 50, B < 27
(b) A > 25, B < 17
(c) A < 5, B > 17
(d) A > 15, B > 47

Ans. c
BOD values of clean water (A) is less than 5 ppm
So, A < 5
BOD values of polluted water (B) is greater than 17 ppm
So, B > 17
So, Ans. is (c)

Q.15. In stratosphere most of the ozone formation is assisted by : [JEE Main 2021]
(a) cosmic rays
(b) γ-rays
(c) ultraviolet radiation
(d) visible radiations

Ans. c
Ozone in the stratosphere is a product of UV radiations acting on dioxygen (O₂) molecules. 

Q.16. The gas 'A' is having very low reactivity reaches to stratosphere. It is non-toxic and non-flammable but dissociated by UV-radiations in stratosphere. The intermediates formed initially from the gas 'A' are : [JEE Main 2021]
(a)
(b)
(c)
(d)

Ans. d
In stratosphere CFCs get broken down by powerful UV radiations releasing cl^.

Q.17. Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). [JEE Main 2021]
Assertion (A) : Photochemical smog causes cracking of rubber.
Reason (R) : Presence of ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate in photochemical smog makes it oxidizing.
Choose the most appropriate answer from the options given below :
(a) Both (A) and (R) are true but (R) is not the true explanation of (A)
(b) (A) is false but (R) is true.
(c) (A) is true but (R) is false.
(d) Both (A) and (R) are true and (R) is the true explanation of (A)

Ans. d
Photochemical smog causes cracking of rubber, the common component of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyel nitrate (PAN).

Q.18. Which one of the following statements is NOT correct? [JEE Main 2021]
(a) Eutrophication indicates that water body is polluted
(b) The dissolved oxygen concentration below 6 ppm inhibits fish growth
(c) Eutrophication leads to increase in the oxygen level in water
(d) Eutrophication leads to anaerobic conditions

Ans. c
Eutrophication leads to decrease in oxygen level of water.
3^rd statement is incorrect.

Q.19. Given below are two statements : [JEE Main 2021]
Statement I : Chlorofluoro breakdown by radiation in the visible energy region and release chlorine gas in the atmosphere which then reacts with stratospheric ozone.
Statement II : Atmospheric ozone reacts with nitric oxide to give nitrogen and oxygen gases, which add to the atmosphere.
For the above statements choose the correct answer from the options given below :
(a) Statement I is incorrect but Statement II is true
(b) Both Statement I and II are false
(c) Statement I is correct but Statement II is false
(d) Both Statement I and II are correct

Ans. b
Statement (1)
CFCs are broken down by powerful UV radiation and releases chlorine free radical which reacts with ozone and start chain reaction.

Statement (2)
Atmosphere ozone reacts with nitric oxide to produce nitrogen dioxide and oxygen.

Q.20. Which one of the following gases is reported to retard photosynthesis?
[JEE Main 2021]
(a) CO
(b) CFCs
(c) CO₂
(d) NO₂

Ans. d
According to NCERT only NO₂ from the given options can retard the photosynthesis process in plants. 

Q.21. The statements that are TRUE : [JEE Main 2021]
(A) Methane leads to both global warming and photochemical smog
(B) Methane is generated from paddy fields
(C) Methane is a stronger global warming gas than CO₂
(D) Methane is a part of reducing smog
Choose the most appropriate answer from the options given below :
(a) (A), (B), (C) only
(b) (A) and (B) only
(c) (B), (C), (D) only
(d) (A), (B), (D) only

Ans. a
CH₄ causes global warming and also a constituent of photochemical smog.
It is a part of oxidising smog.
CH₄ is generated from paddy fields.
Due to high heat capacity, CH₄ is a stronger global warming causing gas than CO₂. 

Q.22. Which of the following statement(s) is (are) incorrect reason for eutrophication?
[JEE Main 2021]
(A) excess usage of fertilisers
(B) excess usage of detergents
(C) dense plant population in water bodies
(D) lack of nutrients in water bodies that prevent plant growth
Choose the most appropriate answer from the options given below :
(a) (A) Only
(b) (B) and (D) only
(c) (C) only
(d) (D) only

Ans. d
Nutrient enriched water bodies support dense plant populations. This is because of the excess usage of fertilizers and detergents. This process is known as eutrophication.

Q.23. Reducing smog is a mixture of : [JEE Main 2021]
(a) Smoke, fog and O₃
(b) Smoke, fog and N₂O₃
(c) Smoke, fog and CH₂ = CH − CHO
(d) Smoke, fog and SO₂

Ans. d
Classical smog occurs in a cool humid climate, it is a mixture of smoke, fog, and SO₂. It is known as reducing smog. 

Q.24. The green house gas/es is (are) : [JEE Main 2021]
(A) Carbon dioxide
(B) Oxygen
(C) Water vapour
(D) Methane
Choose the most appropriate answer from the options given below :
(a) (A) and (C) only
(b) (A) and (B) only
(c) (A), (C) and (D) only
(d) (A) only

Ans. c
Greenhouse gases are CO₂, CH₄, Water vapour, Nitrous oxide, CFCs and ozone. 

Q.25. The type of pollution that gets increased during the day time and in the presence of O³ is: [JEE Main 2021]
(a) Oxidising smog
(b) Global warming
(c) Acid rain
(d) Reducing smog

Ans. a
Photochemical smog occurs in warm, dry, and sunny climates. It is also called oxidizing smog. The main components of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde, and PAN.

Q.26. The presence of ozone in troposphere: [JEE Main 2021]
(a) protects us from greenhouse effect
(b) protects us from the UV radiationp
(c) protects us from the X-ray radiation
(d) generates photochemical smog

Ans. d
Ozone is a strong oxidising agent like NO₂. In troposphere both O₃ and NO₂ react with the unburnt hydrocarbons to produce the chemical components of photochemical smog, like formaldehyde (HCHO), acrolein (CH₂ = CH - CHO) and PAN or peroxyacetyl nitrate.
Hence, in troposphere, the presence of ozone generates photochemical smog.

Q.27. Given below are two statements : [JEE Main 2021]
Statement I : An allotrope of oxygen is an important intermediate in the formation of reducing smog.
Statement II : Gases such as oxides of nitrogen and sulphur present in troposphere contribute to the formation of photochemical smog.
In the light of the above statements, choose the correct answer from the options given below:
(a) Statement I is false but Statement II is true
(b) Both Statement I and Statement II are false
(c) Both Statement I and Statement II are true
(d) Statement I is true but Statement II is false

Ans. b
Reducing smog as is acts as reducing agent, the reducing character is due to presence of sulphur dioxide and carbon particles.

Q.28. Given below are two statements : [JEE Main 2021]
Statement I : The value of the parameter "Biochemical Oxygen Demand (BOD)" is important for survival of aquatic life.
Statement II : The optimum value of BOD is 6.5 ppm.
In the light of the above statements, choose the most appropriate answer from the options given below :
(a) Statement I is false but Statement II is true
(b) Statement I is true but Statement II is false
(c) Both Statement I and Statement II are true
(d) Both Statement I and Statement II are false

Ans. b
Clean water would have BOD value of less than 5 ppm whereas highly polluted water could have a BOD value of 17 ppm or more.
Hence, the value of parameter ‘BOD’ is important for survival of aquatic life but optimum value of BOD is 17 ppm or more. So, statement II is incorrect.

Q.29. Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R. [JEE Main 2021]
Assertion A : Hydrogen is the most abundant element in the Universe, but it is not the most abundant gas in the troposphere.
Reason R : Hydrogen is the lightest element.
In the light of the above statements, choose the correct answer from the options given below:
(a) Both A and R are true but R is NOT the correct explanation of A
(b) Both A and R are true and R is the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true.

Ans. b
As we know, hydrogen is most abundant element in the universe but the most abundant gas in the troposphere is nitrogen, because hydrogen is lightest element.
Troposphere contains 3 quarters of mass of the entire atmosphere. The air here contain 78% nitrogen and 21% oxygen. The last 1% is made of argon, water vapour and carbon dioxide.

Q.30. The gas released during anaerobic degradation of vegetation may lead to :
[JEE Main 2021]
(a) Ozone hole
(b) Corrosion of metals
(c) Acid rain
(d) Global warming and cancer

Ans. d
Methane (CH₄) gas is evolved due to anaerobic degradation of vegetation which causes global warming and cancer. It is a heat trapping gas that forces the planet to warm drastically and quickly.