In our country, the legal age for marriage is 18 years for girls and 21 years for boys. This is because teenage mothers are not prepared mentally or physically for motherhood. Early marriage and motherhood cause health problems in the mother and the child.

Convex lens is thicker in centre.

Sound needs a medium for propagation. Take a metal or glass tumbler. Place a cellphone in it. Ask your friend to give a ring on this cellphone. Listen to the ring carefully. Now surround the rim of the tumbler with your hands. Suck all the air of the tumbler. Once again make a ring in cellphone. Sound will completely stop because air has been removed completely from the vessel and forms vacuum. Hence sound needs a medium for propagation.

Since the pole star is situated in the direction of the Earth's axis, so it does not appear to move.

A force that appears due to physical contact of two objects is called contact force.

When the clothes of a person catch fire the person is covered with a blanket to extinguish fire because blanket cuts off the supply of air, that is the supporter of fire.

(i) This 'pop-up' sound indicates the presence of hydrogen gas.
(ii) We conclude that metal reacts with sodium hydroxide to produce hydrogen gas.

Carbon dioxide (CO₂) is majorly responsible for greenhouse effect

Three liquids which can conduct electricity are.
(i) Tap water
(ii) Lemon juice (citric acid)
(iii) Vinegar (acetic acid).

Rough surfaces have more irregularities.

Group X- Lays eggs in water Group Y- Lays eggs on land.

III. The trees of a forest are cut down.
I. The roots of the trees no longer have a firm grip on the soil
II. Rainfalls onto the ground.
IV. The loose soil gets washed away into a nearby body of water.

In the given structure mushroom and beetle have been classified wrongly because mushroom is a multicelled organism and beetle is a Single celled organism.

Burning of plastics and synthetic fabrics produces lots of poisonous gases causing air pollution.

The substances produced by destructive distillation of coal are coke, coal tar and coal gas

Viruses are cellular tiny microscopic organisms that can develop only inside the cells of host organisms.

The soil is loosened before seeds are sown because it allows the roots to penetrate deep into the soil and also helps the roots to breathe.

The traditional ways of purifying water to make it fit for drinking are as follows :
(i) By filtering: This is a physical method of removing impurities. A popular household filter is a candle type filter.
(ii) By boiling : When water is heated, it boils at a temperature of 100°C.At this high temperature, all the harmful micro-organisms or germs present in water are killed and it becomes absolutely safe for drinking. Many households use boiling as a method for obtaining safe drinking water.

The construction of a kaleidoscope :
(i) Get three rectangular mirror strips each about 15 em long and 4 cm wide.
(ii) Join them together to form prism.
(iii) Fix them in a circular cardboard tube or a tube of thick chart paper.
(iv) Make sure that the tube is slightly longer than the mirror strips.
(v) Close one end of the tube by a cardboard dice having a hole in the centre through which we can see.
(vi) To increase durability paste a piece of transparent plastic sheet under the cardboard disc.
(vii) At the other end touching mirror fix a circular plane glass plate.
(viii) Place several small pieces of coloured glass bangles this glass plate.
(ix) Close this end of the tube by a ground glass plate. Keep enough space between the pieces to move around.

Pressure exerted by liquids and gases on the wall of container can be explained by the following experiments. Take a plastic bottle. Fix a cylindrical glass tube (a few ems long) near its bottom. Make sure that the water does not leak from the joint. Cover the mouth of glass tube with a thin rubber sheet. Fill the bottle up to half with water. The bulging of the rubber sheet in this case indicates that water exerts pressure on the sides of container or we can say that liquid exerts pressure on the walls of container. In the case of gas, when we inflate a balloon the balloon will be filled with air and air exerts pressure and its shape has changed. So we find that gases, too, exert pressure on the walls of their container.

Cloning is the production of an exact copy of a cell any other living part, or a complete organism. Ian Wilmut and his colleagues at the Roslin Institute, Edinburgh, Scotland successfully cloned a sheep named Dolly.
Following steps were involved in cloning:
(i) A cell was collected from the mammary gland of a female sheep.
(ii)An egg was obtained from a Scottish blackface and its nucleus was removed.
(iii)The nucleus from the mammary gland cellof Dorset sheep was introduced in the egg.
(iv)This egg was then implanted in the uterus.

1. Fossil Fuels
2. Refining
3. Coke
4. Petrol
5. Coal
6. Diesel
7. Bitumen
8. Petroleum

Precautions while handling the equipments containing mercury are as follows:
(i) Mercury, a liquid metal with high density, can corrode the skin if it drops over it. Hence, the vessel should be closed or tightly packed.
(ii) It should not be heated directly

(a) If Ram touched the heated electric bulb, then his hands could get a serious burn and he would not be able to perform the experiment again with the same desire.
(b) Since aluminium is a good conductor of electricity and mostly, it has been seen that aluminium wires are used for performing the experiment instead of wires without having PVC coating on them.
(c) Ram's teacher has a great concern towards Ram, so that he can perform the experiment carefully and can get its fruitful conclusion

When a fine powder sprinkled on the carrom board and a few drops of oil are poured on the hinges of a door, the door moves smoothly. A cycJe or a motor mechanic some times uses grease between the moving parts of the cycle. In all the above cases, our try was to reduce friction in order to increase efficiency.
Also, interlocking of irregularities is avoided to a great extent due to which the movement becomes smooth. The substances which reduce friction are called lubricants. In some machines, it may not be advisable to use oil as lubricant. There is an air cushion between the moving parts, that is used to reduce friction.

Body changes during adolescence are given below

Difference between a natural and an artificial satellite.

Applications of artificial satellites are
(i) These kinds of satellites are used for weather for casting such as rainfall, snowfall, etc.
(ii) For communication purpose such as long distance transmission of telephone calls, TV programmes, internet the artificial satellites are used.
(iii) The natural sources of earth are usually surveyed by the artificial satellites.

(a) String of sitar is a vibrating part of sitar.
(b) Since if we beat the dholak, then the membrane of dholak starts vibrating with high amplitude and as a fact, the loudness is directly proportional to the square of amplitude. Therefore, in the form of the loudness created by beating dholak
(c) The sound wave produced by flute is regular curving. So, there is no part of noise.Thus, we hear shrilling sound of flute.
(d) The values displayed by Anjali's grandfather are scientific methods and critical thinking.

Since ebonite rod acquires charge when rubbed. So, the Charge transfer will be either too less or there will be no transfer of charges, so the strips of aluminium will not be wider and we are not able to predict the object whether it is charged or not.

When the forest trees are cut down, then the lesser number of trees put less water vapour into atmosphere through transpiration. Since, less water vapour is put into the atmosphere, there is less rainfall in that area.
When there is less rainfall in an area, then less water percolates into the ground. Due to this, the groundwater level also gets lowered.
The shortage of surface water (in ponds, lakes, etc) and groundwater due to persistent low rainfall in an area can lead to droughts.
Deforestation also leads to a decrease in the water holding capacity of the soil. The movement of water from the soil surface into the ground is reduced. So, there are floods.

Brick and cell are considered one and the same.
The arrangement of cells is comparable to bricks of a building. As bricks are assembled to make a building, similarly, cells are put together to make
the body of an organism.
Just as cells are the basic structural unit of an organism, bricks are the structural unit of a building.
Also, as buildings may differ in designs, shapes and sizes but are made up of bricks. In the same way, organisms may differ from one another (e.g. a human, a dog and a plant) but all of them are made up of cells

Reasons of forest fires are
(i) At high temperature, sometimes dry grass catches fire which spreads throughout the forest.
(ii) Campfire may also be a reason.
(iii) Lightning.
(iv) The use of fires by villagers to ward off wild animals.
(v) Fire lit intentionally by people living around forests for recreation.
(vi) Fires started accidentally by careless visitors to forests how discard cigarette butts.
(vii) The friction of bamboos due to high wind velocity and rolling stones.

(a) Nikita was aware that plastic is a non-biodegradable material. Disposal of plastic is a major problem. It is not easily decomposed by natural process. So, to avoid the use of plastic she prefer to take steel lunch box.
(b) No, plastic materials are not environment friendly since, it takes several years to decompose and causes environmental pollution. Besides, in the burning process it releases lots of poisonous fumes (gases) into the atmosphere causing air pollution.
(c) Nikita is very aware, sensible and intelligent girl.

(a) Cholera By maintaining personal hygiene and good sanitation practices.
(b) Typhoid Eating properly cooked food, drinking boiled water and by getting vaccinated against the disease.
(c) Hepatitis-A Drinking boiled water and getting vaccinated against the disease

(a) The practices used in field which are not environment friendly are use of fertilisers, pesticides, weedicides these are chemical substances that pose health hazards. Tractor though saves labour and time but contributes to air pollution.
(b) Modern agricultural implements save both time and labour as compared to traditional equipments.
(c) The example of weedicide is 2,4-D. The precaution taken by farmers, while spraying it on crops is they should properly cover their nose and mouth, so as to avoid inhaling of these chemicals.

(i) The symptoms observed in the villagers show that oxides of nitrogen and sulphur must be coming out of the chimney. This is due to the combustion of fossil fuels like coal, oil, natural gas etc. to produce high temperature at which oxidation of atmospheric nitrogen takes place.
(ii) Sheela is aware, helpful and intelligent woman.

(i) Rahul had food poisoning.
(ii) It could be due to micro-organisms like fungi and bacteria that were present on uncovered rice.
(iii)The doctor is helpful, considerate and intelligent.

False, sun's rays do warm the earth's surface. This is infact necessary for existence of life on earth.

It is not clear from the diagram that what is A and B. 'So, we cannot predict the actual solution. But if we compare with NCERT activity, this seems to be a potato and correct diagram is A because positive terminal makes the green spot on the potato.

Yes, there is always a force of friction between the wheels of a moving train and iron rails. The name of this friction is rolling friction, since, the wheels are rolling on the track. On introducing air cushion, the frictional force becomes less, since there is no contact between rails and wheels.

Laser light comes from a very small hole and the lens of the laser light is also very small, so the light will penetrate into one part of the eye and it can injure the retina, whereas the normal torch spreads out the light which does not cause any harm to our eyes.
So, the beam of laser light should not be used to perform an activity.

When sun is shifting towards the south, then it is called dakshnayan and when the sun shifts towards the south, it is called uttarayan. So, the Sun shifts towards the south from 21 st June and it starts shifting towards north from 22nd December.

(a) No, Rukmini's mother-in-law was absolutely wrong in blaming her.
(b) The sex of a child is determined by the father as the sperm (either X or Y) comes from him. The mother always contributes an X-chromosome as an egg has only X-chromosome.
(c) Rukmini's daughter is caring, intelligent, logical and has scientific aptitude.

According to me, Raman is very curious to know about science.

(a) A-sperm, B-ovum (egg).
(b) The process is fertilisation.
(c) During the process, the sperm nucleus fuses with the egg nucleus to form the zygote.

Since, during thundering, negative charges get accumulated near the clouds and positive charges accumulate near the ground. So, when these charges meet, then electric discharge takes place between ground and clouds. So, a large amount of energy is released in the form of thunder and lightning.

Since, range of vibrations is different by different objects. But we can hear the vibrations which lies between 20 Hz to 20,000 Hz, so sound of every vibration cannot be heard by us.

The nuclear structure of plant and animal cells is same but the nucleus of bacterial cell is different. It is not well organised. It and does not have nuclear membrane and nucleolus. The genetic material is present in special region. Therefore, bacteria is called prokaryotes while plants and animals are eukaryotes.

Some tribals depend on the jungle because they get almost of their resource to live from the jungle like shelter, wood, food, etc.

Magnesium is found in plants in the form of ionic salts in chlorophyll. Due to its deficiency, plants are unable to produce enough chlorophyll and as a result, leaves develop yellowish colour.

The biodegradable articles are
(a) paper
(b) woollen clothes
(c) wood
(f) peels of vegetables

These resources are present in an unlimited quantity in nature and are not likely to be exhausted by human activities.