In green chemistry, the reactions are generally carried out in the presence of mild and environment friendly reagents, such as ultraviolet light, sound waves, enzymes and microwaves so that harmful chemicals are neither used up nor released. Hence green chemistry acts as a tool for reducing environmental pollution.

1. He felt laxative effect.
2. The laxative effect is observed when the sulphates present in water have concentration greater than 500 ppm. Otherwise at moderate levels it is harmless.

(i) Recycling
(ii) Burning and incineration
(iii) Sewage Treatment
(iv) Dumping

(i) Ozone is thermodynamically unstable and decomposes bask to molecular oxygen before reaching near earth's surface.
(ii) As negligible amount of UV - rays reach near the surface the formation of ozone near the surface of earth is rare.

1. The main reason of ozone layer depletion is due to the release of chlorofluorocarbons (CGCs), also known as freons.
2. These compounds are non - reactive, non - flammable, non - toxic organic molecules and therefore used in refrigerators, air - conditioners, in the production of plastic foam and by the electronic industry for cleaning computer parts, etc.

(i) The water pollutants originate from both natural and human activities. The source of water pollution is classified as Point and Non-point source
(ii) Easily identified source of place of pollution called as point source. Example: municipal and industrial discharge pipes
(iii) Non-point source cannot be identified easily. 
Example: agricultural runoff, mining wastes, acid rain, and storm-water drainage and construction sediments.

VIABLE PARTICULATE	NON-VIABLE PARTICULATE
i) The viable particulates are the small size living organisms.	The non-viable particulates are small solid particles and liquid droplets suspended in air
ii) Eg: Bacteria, fungi moulds, algae, etc.,	Eg : Fly ash, cement dust, oil smoke, fumes etc.,

Acid rain causes extensive damage to buildings and structural materials of marbles. This attack on marble is termed as stone leprosy.
CaCO₃ + H₂SO₄ ⟶ CaSO₄ + H₂O +CO₂↑

The heating up of earth through the greenhouse effect is called global warming. Although the greenhouse effect is a naturally occurring phenomenon, it is intensified by the continuous emission of greenhouse gases into the atmosphere. During the past 100 years, the amount of carbon dioxide in the atmosphere increased by roughly 30 percent and the amount of methane more than doubled. If these trends continue, the average global temperature will increase which can lead to melting of polar ice caps and flooding of low lying areas. This will increase incidence of infectious diseases like dengue, malaria, etc

When ultraviolet radiations reach dioxygen molecule: in stratosphere, two free oxygen atoms are produced. II These oxygen atoms combine with dioxygen I molecule and forms ozone
\(O_{2(g)}\xrightarrow{UV}O_{}(g)+O_{(g)}\)
\(O_{(g)}+O_{2(g)}\overset{UV}\leftrightharpoons O_{3(g)}\)

Since the photochemical smog is formed as a result of photochemical reaction between oxides of nitrogen: and hydrocarbon, hence it is name so.

(i) Green chemistry is a chemical philosophy encouraging the design of products and Processes that reduce or eliminate the use and generation of hazardous substances.
(ii) For this, scientist are trying to develop methods to produce eco-friendly compounds. This can be best understood by considering the following example in which styrene is produced both by traditional and greener routes. To avoid carcinogenic benzene, greener route is to start with cheaper and environmentally safer xylenes.
(iii) Green chemistry means science of environmentally favourable chemical synthesis.

At high altitudes to the atmosphere consists of a layer of ozone (O₃) which acts as an umbrella or shield for harmful UV radiations. It protects us from harmful effect such as skin cancer. UV radiation can convert molecular oxygen into ozone as shown in the following reaction.

Ozone gas is thermodynamically unstable and readily decomposes to molecular oxygen.

Smog is a combination of smoke and fog which forms droplets that remain suspended in the air. Smog is a chemical mixture of gases that forms a brownish yellow haze over urban cities. Smog mainly consists of ground level ozone, oxides of nitrogen, volatile organic compounds, SO₂, acidic aerosols and gases, and particulate matter.

There may be exercise concentration ( > 500 ppm) of sulphates in the ground water. So he could have felt laxative effect.