Water can be made safe for drinking by following ways:
(i) Water is filtered. Many filters available in the markets are used by people.
(ii) Some use boiling as a method for obtaining safe drinking water because boiling kills the germs present in the water.
(iii) Chlorination is a chemical method for purifying water.

Many industries discharge harmful chemicals into rivers and streams. For example, oil refineries, paper factories, textile, sugar mills and chemicals factories. The chemicals released include arsenic, lead and fluorine which lead to toxicity in plants and animals. Soil is also affected by impure water, causing changes in acidity, growth of worms etc.

The instrument which is used to detect a charged body is an electroscope.

Construction
(i) Take an empty jam bottle.
(ii) Take a piece of cardboard slightly bigger in size than the mouth ot t~e bottle.
(iii) Pierce a hole in it so that a metal paper clip can be inserted.
(iv) Open out the paper clip.
(v) Cut two strips of aluminium foil about 4 x 1 cm each. Hang them on paper clip.
(vi) Insert the paper clip in the cardboard so that it remains perpendicular to it.
(vii) Charge a refill and touch it with the end of the paper clip.
Working
(i) The aluminium foil strips receive the same charge from the charged refill through the paper clip. The strips carrying same charge repel each other, they become wide open.
(ii) Touch the end of paper clip gently with hand and we will find a change in the foil strip. Repeatition gives the same result.

Plastic is non-biodegradable, it takes several years to decompose. Thus cause environmental pollution. So, we should avoid use of plastics

(a) Fertiliser
(b) Crop
(c) Ploughing or Tilling
(d) Pisciculture

(1) Cornea
(2) Iris
(3) Eye lens
(4) Ciliary muscles
(5) Sclera
(6) Blind Spot.

Pollutants in air are discolouring white marble of Taj Mahal. The Mathura Oil Refinery near Agra as well as various industries in and around Agra are emitting gaseous pollutants such as sulphur dioxide and nitrogen dioxide into the air which cause acid rain. Acid rain corrodes the marble (CaCOJ of the monuments Suspended particulate matter such as the soot particles emitted by Mathura Oil refinery has contributed towards the yellowing of the Marble. The Supreme Court of India ordered all the industries in Agra area to switch over to cleaner fuels like CNG and LPG to reduce air pollution.

1. Seismograph,
2. Richter,
3. Earthquake,
4. Conduction.

Plastic is non-biodegradable and causes environmental pollution as it takes several years to decompose. It is not environment friendly. When the plastic waste materials are burnt, they burn very slow. They do not get completely burnt. In the burning process, they release lots of poisonous fumes (gases) into the atmosphere causing air pollution. The animals eat up the polythene bags and wrappers of food along with the leftover food thrown on garbage dumps.
The methods to limit its consumption are:
Reducing its use; reusing it for some other purposes and recycling. It may reduce environmental pollution also.

(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) While entering the cinema hall along with her friends, pupil of Pooja's eyes gets expanded due to which for few minutes she was unable to see the things around her. On the other hand, when she made on exit fromthe mall, at that moment, her pupil of her eyes becomes contracted and a large amount of light entered in her eyes due to which she felt discomfort to get things around her. But after few minutes, the pupil size starts increasing and she was able to observe the surroundings.
(b) Pooja seems to be very intelligent and conscious minded as she wore her goggle at the same time when she was feeling discomfort due to the large amount of light coming through the sun rays.

We know that (time period)2  ∝ (radius of orbit)3
\({ T }_{ 1 }^{ 2 }={ Kr }_{ 1 }^{ 3 }\)                     . . . (i)
\({ T }_{ 1 }^{ 2 }={ Kr }_{ 2 }^{ 3 }\Rightarrow { T }_{ 2 }^{ 2 }=\left( \frac { { r }_{ 1 } }{ 2 } \right) ^{ 3 }\)          .... (ii) \(\left[ \because { r }_{ 2 }=\frac { { r }_{ 1 } }{ { r }_{ 2 } } \right] \)
\(\frac { { T }_{ 1 }^{ 2 } }{ { T }_{ 2 }^{ 2 } } =\frac { { r }_{ 1 }^{ 3 } }{ { r }_{ 1 }^{ 3 } } \times 8\)
⇒ \({ T }_{ 2 }^{ 2 }=\frac { { T }_{ 1 }^{ 2 } }{ 8 } \)
⇒ \({ T }_{ 2 }=\frac { 1 }{ 2\sqrt { 2 } } \)
It means that time period reduces by \(\left( \frac { 1 }{ 2\sqrt { 2 } } \right) \) factor.
So, the days in a year will be approx. 129 instead of 365 days.

The tail of the comet is always directed away from the Sun. The tail will be longest in the position B because the tail is visible only when the comet passes through the inner solar system and B is nearest.

It is not safer to use wired telephone during lightning because at that time lightning can enter the wire of telephone, if open somewhere, that is if there is any cut in the wire. On the other hand, there cannot be any possibility of this type in wireless telephone.

(a) We will find seedlings in all the glasses.
(b) Glass B shows maximum growth as it contained urea which is a rich source of nitrogen.
(c) Manures and fertilisers are essential for better growth of plants.
(d) Manure is a natural substance obtained by the decomposition of animal and plant residues.
(e) Soil fix up the plant. It also retains water for plant absorption.

Lack of vitamin A in food stuff is responsible for many eye troubles. Most common among them is night blindness. One should, therefore, include in the diet components which have vitamin A. Raw carrots, broccoli, green vegetables and cod liver oil are rich in vitamin A. Eggs, milk, curd, cheese, butter and fruits such as papaya and mango are also rich in vitamin A.

The Ganga is said to be the only holy river in India. It sustains most of the northern, central and eastern Indian populations. Recently a study by World Wide Fund (WWF) reports that the Ganga is an endangered river. The towns and cities through which it passes throw large quantities of garbage, untreated sewage, dead bodies etc. which make river dead. A plan launched in 1985 to save this river is Ganga Action Plan.

Sometimes we see bright streaks of light in the sky. These are commonly known as shooting stars, although they are meteors. It is usually a small object that occasionally enters into the Earth atmosphere. At the time when they are at high speed, due to friction they glow and evaporate quickly. Hence, bright streak lasts for a very short time.

The process of transferring of charge from a charged object to the earth is called earthing. It is provided in buildings to protect us from electrical shocks due to any leakage of electric current.

It is done by sickle or by a machine called harvester.

Infrared radiation is absorbed by CO₂

Since angle of incidence = angle of reflection. So, angle of incidence = 30°

13 times, because the earth makes 1 revolution around the sun in 1 year.

The tremors produce waves on the surface of the earth. These waves are called seismic waves.

Jute fibres are obtained from stem of jute plant.