1)What are the different ways in which water gets contaminated?
ANSWER:-The different ways in which water gets contaminated are Industrial
wastes, agricultural waste and sewage waste.
2)At an individual level, how can you help reduce air pollution?
ANSWER:-An individual can reduce air pollution by:
(i) Avoiding the use of cars as much as possible and by using
public transport whenever possible.
(ii) By not using vehicles for short distances.
(iii) By using clean fuels such as LPG and CNG instead of diesel
and petrol.
(iv) Always disposing the garbage properly and not burning it.
3) Clear, transparent water is always fit for drinking. Comment.

ANSWER:-No. Clear and transparent water is not always fit for drinking. Water might appear clean, but it may contain
some disease causing micro-organisms and other dissolved impurities. Hence, it
is advised to purify water before drinking.

4) You are a member of the municipal body of your town. Make a
list of measures that would help your town to ensure the supply of clean water
to all its residents.
ANSWER:-To ensure
the supply of clean water to all residents the following steps must be taken:
(i) The main water source must be built in clean surroundings and
should be maintained properly.
(ii) Chemical methods such as chlorination must be used for
purifying water.
(iii) The area around water pipes must also be clean.
5)Explain the differences between pure air and polluted air.
ANSWER:-pure air-Free from harmful and poisonous gases, Fit for breathing
and good for health, Pure air is good for crop production and wild life.
Polluted Air- Increased levels of harmful and poisonous gases, Unfit for breathing and may cause diseases like asthma,
cancer etc, Polluted air is a threat to our
ecosystem. It affects crops, wild life as well
as aquatic life.
6)Explain circumstances leading to acid rain. How does acid rain
affect us?
ANSWER:-Burning of fossil fuels such as coal and diesel releases a variety
of pollutants such as sulphur dioxide and nitrogen dioxide into the atmosphere.
 These pollutants react with water vapours present in the
atmosphere to form sulphuric acid and nitric acid respectively. These acids
come down with the rain, thereby resulting in acid rain.

Effects of acid rain:
(i) Acid rains damage crops.
(ii) Acid rains corrode buildings and structures especially those
made of marble such as Taj Mahal.

7) Which of the following is not a greenhouse gas?
(a) Carbon dioxide
(b) Sulphur dioxide
(c) Methane
(d) Nitrogen
ANSWER :-(d) Nitrogen
8) Describe the ‘Greenhouse Effect’ in your own words.
ANSWER:-Green House effect is a process by which solar radiation is
absorbed by green house gases and is transmitted to all directions. This
increases the temperature of the surroundings
and is responsible for global warming. Gases like CO2.
10) Describe the threat to the beauty of the Taj Mahal.

ANSWER:-The industries located around Agra like rubber processing,
automobile, chemicals and especially the Mathura oil refinery, were
producing pollutants like sulphur dioxide and nitrogen
dioxide, thus forming acid rain. It corroded
the marble of Taj Mahal monument. The suspended particles and ash (soot) from
Mathura refinery caused yellowish colour to Taj

11) Why does the increased level of nutrients in the water
affect the survival of aquatic organisms?
ANSWER:-An increase in the level of nutrients in a water body leads to an
excessive increase in the
population of algae
in the water body. When these algae die, they serve as food for decomposers. A
lot of oxygen is utilised in this process,
consequently leading to a decrease in the level of oxygen dissolved in the
water body. 
This in turn causes fishes and other aquatic organisms to die.