Algal bloom is caused by the enrichment of nutrients in the water body. The nutrients from the fertilisers, etc cause rapid growth of algae. It affects in following ways:
(i) Deteriorate the water quality.
(ii) Lead to death of aquatic organisms

Industries oil refineries, paper factories produce toxic chemicals that are often discharged into rivers or streams, thereby polluting the water, e.g. The chemicals include pollutants such as arsenic, lead, fluorides, mercury, etc which lead to toxicity in plants and animals.
Effects The water polluted with toxic industrial wastes can kill aquatic animals. On reaching human body, it can damage nervous system and cause disease such as cancer.

This means that air is contaminated by the addition of unwanted and harmful substances which are injurious to living organisms, property or interferes with normal environmental processes. This is called air pollution. The air around us is a mixture of various gases. It is composed of 78% nitrogen,21% oxygen and remaining 1% by CO₂,Ar CH₄, O₃ and water vapour.

The increased level of nutrients in the water increases the growth of algae. Once these algae dies, they serve as food for decomposers like bacteria. A lot of oxygen is utilised in this process, consequently leading to a decrease in the level of Dissolved Oxygen (DO) in the waterbody. This, in turn causes fishes and other aquatic organisms to die.

India's most famous tourist attraction 'Taj Mahal' is located at Agra. It has become a matter of concern in recent years due to increasing air pollution. Taj Mahal is made up of white marble. Experts have warned that air pollution is discolouring its white marble. The industries located around Agra produce pollutants like sulphur dioxide and nitrogen dioxide. These gases react with water vapours to form sulphuric acid and nitric acid respectively. These acids comes down along with rain as acid rain and corrodes the white marble of Taj Mahal. This phenomenon is also called as 'marble cancer'.

Nitrogen is not a greenhouse gas. It is naturally found in the air and is a major constituent of it.

The bacteria present in the faeces are used as indicators of the quality of water.

The quality of air at various locations is monitored regularly by government and other agencies. These data can be used to generate awareness about air pollution among people.

Combustion of fossil fuels generates a lot of air pollution. Solar energy and wind energy are two alternative sources of energy which do not cause any pollution.

Alternative fuels can be used in place of fossil fuels to reduce pollution, e.g. solar energy.

Infrared radiation is absorbed by CO₂

(a) Various sources of water pollution are classified as point sources and non-point sources.
(b) The sources or places of pollution which are easily identifiable are point sources of water pollution.e.g. factories, power plants, etc.
(c) Agricultural run-off and acid rain are non-point sources of water pollution.

(a) It is recommended to stop the vehicle engine at the red light signals to minimise the emissions of poisonous gases like CO, NO, etc from the automobile exhaust.
(b) With the vehicle engine ON, the incomplete combustion of fuel will take place with release of gases like CO.
(c) The government is trying to make people understand the need for reducing environment pollution and the small steps that they can take for environmental protection.
(d) Yes, I will support the message. It is for the common good.
(e) Arjun is keen learner, strong observer and responsible.