Class 11th

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii)

Ozone hole is thinning of the ozone layer of the stratosphere at some places is correct since it was found that a unique set of conditions were responsible for the ozone hole. In summer, nitrogen dioxide and methane react with chlorine monoxide and chlorine atoms forming chlorine sinks, preventing much ozone depletion, whereas in winter, special types of clouds called polar stratospheric clouds are formed over Antarctica. 

Following reactions occur in the stratosphere.

CF₂Cl₂→CF₂Cl + Cl?

Cl? +O₃→ClO? + O₂

ClO? +  [ O ] →Cl? + O₂

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (i) the reaction is endothermic and requires very high temperature is correct since dinitrogen and dioxygen are the main constituents of air. These gases do not react with each other at a normal temperature. The dissociation energy of N₂is very high due to the presence of triple bond and it is very stable. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (ii) Troposphere is correct since the lowest region of atmosphere in which the human beings along with other organisms live is called troposphere. It extends up to the height of  approximately 10 km from sea level. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (ii) i.e., It has low concentration of oxidizing agents is the answer since the common components of photochemical smog are ozone, nitric oxide, acrolein, formaldehyde and peroxyacetyl nitrate (PAN). Photochemical smog causes serious health problems and both ozone and PAN act as powerful eye irritants. Photochemical smog contains high concentrations of oxidants. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii)

i.e., Decrease in the amount of dissolved oxygen in water is the answer since organic waste is oxidized by microorganisms in the presence of dissolved oxygen. Hence, oxygen decreases in water as a result it is harmful for aquatic life. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (i) i.e., rich in dissolved oxygen is the answer since the total amount of oxygen consumed by microorganisms in decomposing organic matter present in a certain volume of water is known as Biochemical Oxygen Demand (BOD) of water. If the BOD value is less than 5 ppm, then the sample of water is considered to be pure and is rich in dissolved oxygen. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (i)

i.e., Its main components are produced by the action of sunlight on emissions of automobiles and factories is the answer since classical smog is a mixture of smoke, fog and sulphur dioxide and occurs in cold humid climates. While the gases released by automobiles and factories are not responsible for classical fog. 

This is a Multiple choice Questions as classified in NCERT Exemplar

Option (iii)

SO₂ is correct since photochemical fog is formed in the presence of sunlight in summers when NO and hydrocarbons are present in large amounts in the atmosphere. SO₂ is not responsible for photochemical fog.