Chapter 14: Environmental Chemistry

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Ans: Option (iii) i.e., Both A and R are not correct is the answer since in cold places, sunlight required to grow plants is less. Due to which plants are kept in a glass house so that sunlight enters in the greenhouse to heat up the soil and plants. The warm soil and plants emit infrared radiations which are partially absorbed and partially reflected by the glass. 

Ans: Option (ii) i.e., Both A and R are correct, but R is not the correct explanation of A is the answer the pH of rainwater is 5.6 because of the presence of hydronium ions produced due to the dissolution of carbon dioxide in rainwater from atmosphere and when the pH of rainwater drops from 5.6, it is being referred as acid rain. This can be shown as-

\[{{\text{H}}_{\text{2}}}\text{O(l)+C}{{\text{O}}_{\text{2}}}\text{(g)}\to {{\text{H}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\text{(aq)}\]

\[{{\text{H}}_{\text{2}}}\text{C}{{\text{O}}_{\text{3}}}\text{(aq)}\to {{\text{H}}^{\text{+}}}\text{(aq)+HC}{{\text{O}}_{\text{3}}}^{-}\text{(aq)}\]

Ans: Option (i) i.e., Both A and R are correct, and R is the correct explanation of A is the answer since a photochemical smog has high concentration of oxidizing agents and is known as oxidizing smog. Two of the pollutants that are emitted are hydrocarbons (unburned fuels) and nitric oxide (NO). When these pollutants build up to sufficiently high levels, a chain reaction occurs from their interaction with sunlight in which NO is converted into nitrogen dioxide and this in turn absorbs energy from the sunlight and breaks up into nitric oxide and free oxygen atoms. This is shown as-

\[\text{N}{{\text{O}}_{\text{2}}}\text{(g)}\xrightarrow{\text{hv}}\text{NO(g)+O(g)}\]

\[\text{O(g)+}{{\text{O}}_{\text{2}}}\text{(g)}\to {{\text{O}}_{\text{3}}}\text{(g)}\]

Ans: Option (ii) i.e., Both A and R are correct, but R is not the correct explanation of A is the answer since the increased amount of carbon dioxide in the air is the main cause for global warming. Excess of carbon dioxide gets released into the atmosphere and is removed by green plants which maintains an appropriate level of carbon dioxide into the atmosphere. 

Ans: Option (iv) i.e., A is not correct, but R is correct since ozone in the stratosphere is a product of ultraviolet radiations falling on oxygen molecules. The main cause of ozone layer depletion is the release of CFCs i.e., freons. With the depletion of the ozone layer, more ultraviolet radiation filters into the troposphere. These radiations lead to ageing of skin, cataract, sunburn, skin cancer etc. 

Ans: Option (i) i.e., Both A and R are correct, and R is the correct explanation of A is the answer since pesticides are the synthetic toxic chemicals with ecological repercussions and their repeated use gives rise to pests that are resistant to that group of pesticides and hence making the pesticides ineffective. Therefore, as insect resistance of DDT increased, other organic toxins such as Aldrin and Dieldrin got introduced in the market by the pesticide industry. Most of the organic toxins are water insoluble and are non-biodegradable. 

Ans: Option (iii) i.e.,  Both A and R are not correct since the amount of oxygen required by bacteria to breakdown the organic matter present in a certain volume of a sample of water, is called BOD i.e., Biochemical Oxygen Demand. If the BOD of the water is < 5 ppm then it is clean but if it increases then the water pollution increases.