Ncert Solutions Chemistry Class 11th

Major Causes of water pollution are:

Pathogens: Pathogens include bacteria and other microorganisms that enter water from domestic sewage and animal excreta.
Human excreta contain bacteria such as Escherichia coli and Streptococcus faecalis, which cause gastrointestinal diseases.

Organic wastes: Organic wastes, when added to water, are decomposed by bacteria, which consume dissolved oxygen in water. When the concentration of dissolved oxygen in water decreases below 6 ppm, the growth of fish is inhibited. The breakdown of organic wastes by anaerobic bacteria produces chemicals that have a foul smell and are harmful to human health.

Chemical pollutants: Some inorganic chemicals as an industrial wastes dissolve in water like cadmium, mercury nickel etc. These metals are dangerous to humans and other animals. These metals can damage kidneys and central nervous system, liver etc. Petroleum products pollute many sources of water.

Depletion of ozone layer creates some sort of holes in the blanket of ozone which surrounds us, this is known as ozone hole.

The consequences are:

1. With the depletion of ozone layer, more UV radiation filters into troposphere. UV radiations lead to ageing of skin, cataract, sunburn, skin cancer, killing of many phytoplanktons, damage to fish productivity etc.
2. It has also been reported that plant proteins get easily affected by UV radiations which leads to the harmful mutation of cells.
3. It also increases evaporation of surface water through the stomata of the leaves and decreases the moisture content of the soil.

     4. Increase in UV radiations damage paints and fibres, causing them to fade faster.

3.30.  (i) For n = 3, the element belong to 3rd period, p-block element.
The electronic configuration is =1s² 2s² 2p⁶ 3s² 3p⁴. The element name is sulphur.

(ii) For n = 4, the element belongs to 4th period and since the valence shell has 4 electrons it belongs to group 4.
Electronic configuration= 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s², and the element name is Titanium (T_i).

(iii) For n = 6, the element belongs to 6th period. Last electron goes to the f-orbital, element is from f-block. It belongs to group = 3
The element is gadolinium (z = 64)
Complete electronic configuration = [Xe] 4 f⁷ 5d¹ 6s².

Harmful effects of photochemical smog: Photochemical smog causes serious health problems. Both ozone and PAN (peroxyacetyl nitrate) act as powerful eye irritants. Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing. Photochemical smog leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.

Control:

• Control of primary precursors of photochemical smog, such as NO2 and hydrocarbons, the secondary precursors such as ozone and PAN, the photochemical smog will automatically be reduced.
• Use of catalytic converter in automobiles prevents the release of nitrogen oxide and hydrocarbons to the atmosphere.

Plants like Pinus, juniparus, quercus, pyrus etc. can metabolise nitrogen oxide thus their plantation could help in this matter.