Class 11th

Green chemistry is a way of thinking and is about utilising the existing knowledge and principles of chemistry and other sciences to reduce the adverse effect of pollution. It is a production process that would bring about minimum pollution or deterioration to the environment. In a nutshell, it is a cost-effective approach which involves reduction in material, energy consumption and waste generation.
It will help in decreasing environmental pollution by adopting the following examples:

1. In a chemical reaction, if reactants are fully converted into useful environmental friendly products by using an environment friendly medium then there would be no chemical pollutants introduced in the environment.
2. During a synthesis, care must be taken to choose starting materials that can be converted into end products with yield approximately up to 100 per cent.
3. It may be worthwhile to carry out synthetic reactions in aqueous medium since water has high specific heat and low volatility. Water is cost effective, non inflammable and devoid of any carcinogenic effects.

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.