Ncert Solutions Chemistry Class 11th

This is a  Short Answers Type Questions as classified in NCERT Exemplar

The atmosphere is divided into certain levels like troposphere, stratosphere, mesosphere, and thermosphere. The stratosphere consists of a considerable amount of ozone, and this protects us from the harmful ultraviolet  radiations coming from the sun. These radiations cause skin cancer in humans. So, it is important to maintain the ozone shield. The main reason for ozone layer depletion is believed to be the release of chlorofluorocarbon compounds (CFCs), also known as Freon. UV radiation can cause genetic mutation and destroy crops, aquatic plants and animals are also affected by ultraviolet radiations.

This is a  Short Answers Type Questions as classified in NCERT Exemplar

Apart from carbon dioxide gas other greenhouse gases are methane, water vapour, oxides of sulphur, nitrous oxide, CFCs, and ozone. Methane is found to be produced naturally when vegetation is burnt, digested, or rotted in the absence of oxygen. Large amounts of methane are released in paddy fields, coal mines, from rotting garbage dumps and by fossil fuels. Chlorofluorocarbons (CFCs) are man-made industrial chemicals used in air conditioning etc. CFCs are also damaging the ozone layer. Nitrous oxide occurs naturally in the environment but is increasing day by day by human activities.

This is a Long Answers Type Questions as classified in NCERT Exemplar

Since the earth's surface is heated by the sunlight, it radiates a part of this energy back to the space as longer Infrared wavelengths and some of the heat gets trapped by CFCs and water vapours present in the atmosphere. They absorb IR radiations and block a large portion of earth's emitted radiations. This radiation, absorbed, is partly remitted to the earth's surface. Therefore, the earth's surface gets heated up by the phenomenon called greenhouse effect.  Thus, the greenhouse effect is defined as the heating up of the earth's surface due to trapping of infrared radiations reflected by the earth's surface by the carbon dioxide layer in the atmosphere. So, the heating up of the earth through the greenhouse effect is called global warming. 

This is a Long Answers Type Questions as classified in NCERT Exemplar

CO₂ gas is confined to the troposphere only and it forms nearly 0.03 per cent by volume of the atmosphere. With the increased use of fossil fuels, a large amount of carbon dioxide gets released into the atmosphere. Excess of carbon dioxide in the air is removed by the green plants and this maintains an appropriate level of it in the atmosphere. Green plants require carbon dioxide for the process of photosynthesis and  which in turn emits oxygen, thus maintaining the balance in nature. Deforestation and the burning of fossil fuels increase the level of carbon dioxide, and this disturbs the balance in the atmosphere. The increased amount of carbon dioxide in the air is mainly responsible for global warming. 

This is a Long Answers Type Questions as classified in NCERT Exemplar

(i) Many techniques are used to control or reduce the formation of photochemical smog. 

(1) If we control the primary precursors of photochemical smog, such as nitrogen dioxide and hydrocarbons, the secondary precursors such as ozone and PAN of the photochemical smog will automatically get reduced.

(2) Mostly catalytic converters are used in automobiles to prevent the release of nitrogen oxide and hydrocarbons to the atmosphere. 

(3) Certain plants e.g., Pinus, Juniparus, Quercus, Pyrus and Vitis metabolise nitrogen oxide and hence their plantation could help in this.

(ii) The organic solvents like- benzene, carbon tetrachloride, toluene etc., are highly toxic in nature. Everyone needs to be careful while using them. For bleaching the cloth hydrogen peroxide is used which is not harmful. Earlier chlorine was used for bleaching the clothes.

(iii) The synthetic detergents are found to be non-biodegradable and hence their use in daily life is to be avoided. Good quality soaps need to be prepared from vegetable oil as they are biodegradable in nature.

(iv) In place of petrol and diesel, the use of CNG and LPG should be preferred as they are pollution free fuels. The other sources such as hydrogen, ethanol etc. can also be used in place of petrol and diesel.