JEE Chemistry Environmental Chemistry MCQs Set 14

Answer: (d) non-biodegradable pollutant

Explanation:
1. DDT is a persistent pesticide that is not broken down by microorganisms.
2. So it is a non-biodegradable pollutant and accumulates in the food chain.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) exosphere

Explanation:
1. The order from the ground upward is troposphere, stratosphere, mesosphere, thermosphere (ionosphere) and exosphere.
2. The exosphere is the outermost layer.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) Mesosphere

Explanation:
1. The temperature falls with height in the mesosphere and reaches about -100 °C at its top, the lowest in the atmosphere.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) troposphere

Explanation:
1. The troposphere is the lowest layer (about 0-10 km) and contains most of the water vapour, clouds and weather.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) NO

Explanation:
1. Jet exhaust releases NO into the stratosphere: \( \ce{NO + O3 -> NO2 + O2} \).
2. The NO is regenerated in a chain and destroys ozone.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) it competes with \( \ce{O2} \) for haemoglobin

Explanation:
1. CO binds to haemoglobin about 200 times more strongly than oxygen, forming carboxyhaemoglobin.
2. This reduces the oxygen carrying capacity of blood.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) CO

Explanation:
1. \( \ce{CO2} \), \( \ce{CH4} \), \( \ce{O3} \), \( \ce{N2O} \), CFCs and water vapour are the greenhouse gases.
2. CO is a poisonous pollutant, not counted as a greenhouse gas.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) Increasing the use of air conditioners, refrigerators and aerosol sprays

Explanation:
1. Refrigeration units, foams and aerosols release CFCs, which are greenhouse gases and ozone depleters.
2. So increasing their use is not a correct approach.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) 5.6

Explanation:
1. Atmospheric \( \ce{CO2} \) dissolves in rain to form carbonic acid, giving a pH of about 5.6.
2. Rain with pH below 5.6 is called acid rain.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) \( \ce{CH4} \)

Explanation:
1. Anaerobic decomposition of organic matter in waterlogged paddy fields produces methane.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) oxides of nitrogen (with hydrocarbons)

Explanation:
1. Sunlight acts on \( \ce{NO2} \) and unburnt hydrocarbons from vehicle exhaust to form ozone, PAN and aldehydes.
2. Hence oxides of nitrogen are the key pollutant.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) Its main components are produced by the action of sunlight on emissions of automobiles and factories

Explanation:
1. Classical smog is a mixture of smoke, fog and \( \ce{SO2} \); it occurs in cold, humid weather and is reducing in nature.
2. Production of smog components by sunlight describes photochemical smog, so (a) is not true.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) Algae

Explanation:
1. Viable particulates are living organisms such as bacteria, fungi, moulds and algae.
2. Fumes, smoke and mist are non-viable.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) Chlorine

Explanation:
1. UV light in the stratosphere breaks C-Cl bonds in CFCs and releases chlorine free radicals.
2. Cl radicals destroy ozone in a chain reaction.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) Chlorine nitrate

Explanation:
1. Chlorine nitrate (\( \ce{ClONO2} \)) and HCl are reservoir species; on polar stratospheric clouds they release active chlorine in spring, causing the ozone hole.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) skin cancer

Explanation:
1. More UV-B radiation reaches the earth, damaging skin cells and causing skin cancer and cataract.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) \( \ce{SO2} \) and \( \ce{CO2} \)

Explanation:
1. NO and freons (CFCs) destroy stratospheric ozone.
2. \( \ce{SO2} \) and \( \ce{CO2} \) do not take part in ozone depletion.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (d) mercury

Explanation:
1. Methylmercury accumulated in fish eaten by the villagers of Minamata Bay, causing nervous system damage.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) sewage pollution

Explanation:
1. E. coli lives in the human intestine, so its presence indicates contamination by sewage.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) a decrease in dissolved oxygen

Explanation:
1. Microorganisms decomposing the organic waste use up the dissolved oxygen.
2. The resulting oxygen shortage kills fish.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (c) kill germs

Explanation:
1. Chlorination disinfects water by killing disease-causing microorganisms.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) water pollution

Explanation:
1. BOD is the oxygen needed by bacteria to decompose organic matter in a water sample, an index of water pollution.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) A dissolved oxygen concentration below 6 ppm is good for the growth of fish

Explanation:
1. Fish need dissolved oxygen above about 6 ppm; below this their growth is inhibited.
2. So statement (b) is not true.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) rich in dissolved oxygen (clean)

Explanation:
1. Low BOD means little decomposable organic matter and hence plenty of dissolved oxygen, i.e. clean water.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) methemoglobinemia (blue baby syndrome)

Explanation:
1. Nitrate is reduced to nitrite in the infant gut; nitrite converts haemoglobin into methaemoglobin which cannot carry oxygen.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (a) dissolved oxygen

Explanation:
1. Nutrient enrichment causes an algal bloom; when the algae die their decomposition consumes dissolved oxygen.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.

Answer: (b) reduce the use and production of hazardous chemicals

Explanation:
1. Green chemistry aims to design processes that minimise or eliminate hazardous substances and waste.

Teacher's Note:
1. Identify the key concept in the question first, then check each option against it.
2. Learn the exceptions to general trends, as they are the most common source of questions.