Eye should be placed at A because only, then \(\angle i=\angle r\).

Hearing impairment means not being able to hear properly. Partial disability is generally the result of a disease, injury or age. Children with impaired hearing need special care by learning sign language. Technological devices for the hearing impaired have made it possible for such persons to improve their quality of life.

The plane of the equator is called the equatorial plane. The plane in which the Earth revolves round the sun is called the orbital plane of the Earth. These two planes are inclined to each other at an angle of 23.5°. This means that the axis of the Earth is inclined to its orbital plane at an angle of 66.5°.

Disadvantages of fertilizers:
(i) They become source of water pollution.
(ii) They make soil less fertile.
(iii) They do not provide any humus to the soil.

Global warming is an increase in the average temperature of the earth's surface. It occurs as a result of increased concentration of greenhouse gases in the atmosphere. The greenhouse gases such as CO₂, CH₄, etc are increasing due to human activities including vehicular emissions, burning of fossil fuels, etc. Global warming has become a major concern for governments worldwide. This is because even as little as 0.5⁰C Crise in temperature can have serious implications.

(a) If Ankush switched on the electric iron rod and (without wearing any footwears), then he could get met with some accident, either in the form of electrical sparking or short circuit of switch board.
(b) Ankush's friend seems to be very intelligent and very much concerned for Ankush as well.

Due to reflection, we can see various objects. Since we know that all surface reflect light, so when light falls on them (any objects), it reflects the light. In this way, this reflected light enters our eyes and due to this, late can see the object.

A book kept on tilted writing desk starts sliding down. The direction of frictional force is in the opposite direction. Thus, frictional force will act in upward direction.

No, in human females, each time during maturation and release of egg, the inner wall of uterus thickens. This thickening of the uterine wall is not permanent.
If the egg gets fertilised, it starts developing and gets embedded in the uterine wall resulting in pregnancy. During pregnancy, no more eggs are released and the thickened lining is discharged only when the baby is born. However, if fertilisation does not occur, the released egg and the thickened lining are shed off resulting in menstruation.

Yes, there will be gravitational force between the astronauts because every object in universe, whether small or large, exerts a force on every other object, it is the universal law of gravitation.

Lightning will not strike the building because all the lightning falling on the building will reside on the surface of the building. Now, there is no need of installing any lightning conductor because all the work of lightning conductor is done by the conducting material itself.

It is necessary to produce large number of eggs and sperms by the animals which reproduce by external fertilisation to enhance the chances of fertilisation.
As the gametes are released in water, many of them may be carried away by movement of water wind, etc or may be eaten by other aquatic animals, so a large number is released to compensate for the loss.

The new species is likely to affect the local species as it poses threats in following manner:
(i) Preying on native species.
(ii) Out competing for food or other resources.
(iii) Causing or carrying disease.
(iv) Preventing native species from reproducing.
(v) Changing food webs.

The structural hierarchy found in organisms starts from the cell that is the basic structural unit in all living organisms. Similar cells combine to form tissues, tissues combine to form organs, organs work together to form organ systems and all the different organ system, combine to form the organism.

(a) When charcoal is burnt, carbon dioxide gas is produced. This gas turns lime water into milky colour. The nature of the gas can be tested by using aqueous solution of carbon dioxide on moist red and blue litmus paper. No effect on red litmus but the solution turns blue litmus to red, so it is acidic in nature .
(b) Equations of all the reactions are given as below:
Carbon + Oxygen\(\rightarrow \) Carbon dioxide 
Carbon dioxide + Lime water \(\rightarrow \) Milky
Carbon dioxide + Water \(\rightarrow \)Carbonic acid
Carbonic acid + Blue litmus\(\rightarrow \) Red litmus

(a) Water is not used to control fires involving electrical equipments because water is a good conductor of electricity. So, it can easily conduct electric current and causes danger of electric shocks.
(b) LPG is a better domestic fuel than wood because LPG has more calorific value and produces no pollution. While wood produces smoke and causes more pollution.
(c) It is because the ignition temperature of paper is less, so it catches fire easily. It does not catch fire, when wrapped around aluminium pipe because aluminium absorbs the heat by conduction, so paper does not attain its ignition temperature

(a) Coal is burnt to heat water and convert it to steam, which then runs the turbines for the generators.
(b) Nikita is environment concerned, conscious of energy usage and tries to think beyond the visible.

Plastic is non-reactive material. When left exposed to moisture and air, it does not react with air and water which are essential for corrosion, therefore does not rust

Antibiotics are tablets, capsules or injections which are used to kill or stop the growth of pathogens, i.e. disease causing microbes. Penicillin, tetramycin are the examples of antibiotics.
Precautions to be taken are
(i) It should be taken in proper doze only on the advice of a qualified doctor.
(ii) Complete course prescribed by the doctor should be taken.
(iii) It should not be taken unnecessarily as it may kill useful bacteria in the body.

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.

Scientific discoveries are a result of hardwork by many people. It can sometimes take long time.

Articles made from nylon are socks, ropes, tents, toothbrushes, car seat belts, sleeping bags etc.

Damaged seeds become hollow and are thus lighter which makes them float.

The substance is oxygen

Black objects appear black because they absorb all the colours, no light is reflected.

No, distilled water does not conduct electricity.

No, friction can never be entirely eliminated. Some irregularities are always there.

The sound which gives a pleasant sensation to our mind is known as the musical sound

In 'tug of war', when two teams pull equally hard, then the rope does not move in any direction.

Forest conservation maintains the balance in nature. It acts as carbon sinks absorbing CO₂ and keeps global warming at bay.

Sketch of human nerve cell is shown as below

Functions of nerve Cells
The nerve cell receives and transfers messages from various body parts to brain and vice-versa and also helps in controlling and coordinating the function of different parts of the body.

No, the bulb will not glow. It is because wood is a non-conductor of electricity.

Carbon monoxide gas is formed as a result of incomplete combustion.

No, we cannot use all our natural resources  forever. All natural resources are going to exhaust.

In the soil, nitrogen is enriched by blue-green algae (cyanobacteria).

Air gets polluted by many reasons. Few of them are as follow:
(i) Vehicles produce high level of pollutants like carbon monoxide, carbon dioxide, nitrogen oxide, smoke etc. These are very poisonous gases. Burning of fuel from vehicles also produces pollution.
(ii) Many industries are also responsible for causing air pollution. Petroleum refineries release polluted gases such as sulphur dioxide, nitrogen dioxide etc. They cause respiratory problems, including lung damage.
(iii)Other kinds of pollutants are CFCs which are largely used in refrigerators, air conditioners and aerosol sprays. Those protect us from ultraviolet rays of the Sun.
(iv) Some human activities like forest fire, burning of fire wood, cow dung cakes, burning of chaff etc. cause air pollution.
(v) Some natural phenomenon like fast dust storms, volcanic eruption produce smoke and dust particles

Forces can be of two types:
(i) Contact forces.
(ii) Non-contact forces.
(i) Contact forces : The forces that come into play when two objects come in contact with each other.
(a) Muscular force: The force which is exerted due to action of muscles is known as the muscular force. e.g., running, bending, walking etc.
(b) Frictional Force: The force responsible for changing the state of motion of an object. Equal and opposite forces are being exerted on an object when its surface comes in contact with other surface. e.g., a car or scooter comes to rest.
(ii) Non-contact forces: The forces that can be exerted from a distance without establishing a contact are called the non-contact forces.
(a) Magnetic forces : Force exerted by a magnet on another magnet or magnetic substances like iron is called magnetic force. e.g., Car sticking to an electromagnet.
(b) Electrostatic force : Force exerted by a charged body on another charged body or uncharged body is called electrostatic force. e.g., If we rub a comb with hair and bring it near some small bits of paper it attracts the bits of paper towards itself. This is electrostatic force.
(c) Force of gravity : The earth pulls every object towards its centre. The force exerted by the earth is called the force of gravity.

Protections against earthquake :
Earthquakes cannot be predicted. They can be highly destructive. It is, therefore, important that we take necessary precautions to protect ourselves all the time. It is advisable to make the structure 'Quake Safe'.
(i) Consult qualified architects and structural engineers.
(ii) In highly seismic area, the use of mud and timber is better. They keep roofs light.
(iii) Fix shelves and cupboards to the walls.
(iv)Be careful where you hang wall clocks, photo frames, water heaters etc.
(v) Building can catch fire during earthquake. So all buildings must have fire fighting equipments in working order.
In the event that an earthquake does strike, take the following steps to protect yourself.
At home: Take shelter under a table, stay away from tall and heavy objects and if you are in bed, do not get up. Protect your head with a pillow.
Outdoors: Find a clean spot, away from buildings, trees, and overhead power lines. Drop to ground. If you are in car or bus do not come out.

Nucleus is the most important component of the living cell. It is round or spherical in shape and situated in the centre of the cell. Nucleus is separated from cytoplasm by a membrane called nuclear membrane. This membrane is porous and allows the movement of materials between the cytoplasm and inner side of the nucleus. There is a small and spherical body in the nucleus. It is called nucleolus. Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. Nucleus also acts as a control centre of the activities of the cell.

(i) Constellations
(ii) Ursa Major
(iii) Remote sensing
(iv) Akash Ganga

In humans, the sound is produced by the voice box or the larynx. Put your fingers on the throat and find a hard bump that seems to move when you swallow. This part of the body is known as the voice box. Belowit is the windpipe. Two vocal cords, are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the passage of air

When the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords may make the cords tight or loose. When the vocal cords are tight and thin, the type or quality of voice is different from that when these are loose and thick.

Deforestation is a major cause which leads to the change in soil properties. Physical properties of the soil get affected by plantation and vegetation. Trees also prevents soil erosion; fewer trees result in more soil erosion. Removal of top fertile layer of soil exposes the lower, hard and rocky layers. This soil has less humus and is less fertile. So, it is not good for plantation. Gradually the fertile land gets converted into deserts, it is called desertification. This way deforestation leads to desertification.

The harmful effects of burning fuels:
(i) Fuels like wood, coal, petroleum etc. which are carbon fuels, produce unburnt carbon particles, which cause respiratory diseases (asthma) and skin diseases.
(ii) Generally CO₂ is released during burning of fuels. It causes the rise in the temperature of the atmosphere of earth, which is called global warming.
(iii)Incomplete combustion of fuel releases many poisonous gases such as carbon monoxide. It can kill people sleeping in a room by causing suffocation.
(iv) Combustion of coal and diesel generates sulphur dioxide. It can kill people sleeping in a room by causing suffocation.
(v) Burning of fuels releases oxides of nitrogen and sulphur. They dissolve in rain water and form acid. Such rain is called acid rain. It is harmful to crops, buildings and soil.

The supply of water to crops at different intervals is called irrigation. Latest irrigation method help us to use water economically. The main methods used are as follows:
(i) Sprinkler system: This system is more useful on the uneven lands where water is available in smaller quantity. The perpendicular pipes, having rotating nozzles on the top, are joined to the main pipe lines at regular intervals. When the water is allowed to flow through the main pipe with the help of a pump, it escapes from the rotating nozzles. It is sprinkled on the crop as if it is raining. Sprinkler is very useful for the sandy soil.
(ii) Drip system: In this system, the water falls drop by drop just at the position of the roots. So it is called drip system. It is the best technique of watering fruit plants, gardens and trees. This system consists of a main pipe to which lateral pipes are joined. The specially prepared nozzles are attached to these lateral pipes. The nozzles are grounded just near the roots of the plants. It provides water to plants drop by drop. Water is not wasted at all. So, it is a boon in regions where availability of water is poor

We take CuS04 solution and dip a pure copper plate as cathode (-ve) and impure copper plate as anode (+ve). Due to voltage of battery, the impurities from the impure sample slowly deposit at the bottom and the copper plate becomes purified .

As friction opposes the relative motion between the two surfaces also produce heat. So, when we rub our hands together vigorously for few minutes, we feel hotness when we strike a matchstick against the rough surface due to which it catches fire. In machineries also, heat is produced due to friction as the machine parts rub against each other.

Kaleidoscope is a cylinder with mirrors containing loose, coloured objects such as beads or pebbles and bits of glass. As the viewer looks into one end, light entering the other creates a colourful pattern due to reflection. Its applications are given below:
(i) It works on the principle of multiple reflections, where several mirrors are placed at an angle (usually 60°) to one another. Typically, these are three rectangular mirrors set at 60° to each other so that they form an equilateral triangle.
(ii) The 60° angle creates seven duplicate images of the objects, 5 at 60° and 2 at 90°. As the tube is rotated, the tumbling of the coloured objects presents varying colours and patterns.
(iii) It is used in decoration purposes, toys, etc.

(i) The figures showing stages during development of embryo are identified as
(a) Embedding of the embryo in the uterus (implantation).
(b) Fertilisation (fusion of egg and sperm).
(c) Zygote formation and development of an embryo from the zygote.
(d) Zygote (showing fusion of gametes) single celled.
(ii) The above stages in sequence are
(b) Fertilisation ⟶ (d) Zygote formation ⟶
(c) Development of embryo ⟶
(a) Implantation of embryo in uterus.
(iii) The embryo after being implanted in uterus, continues to develop and divide and differentiate into body parts. This stage of embryo where body parts are distinct and identified is called foetus. After complete development of foetus, mother gives birth to baby.

We conclude that initially, girls grow faster than boys but by about 18 years of age, both reach at their maximum height. The rate of growth in height varies in different individuals.

(a) A is petroleum and B is natural gas.
(b) A is thick liquid while B is gas.
(c) C is called fractional distillation
(d) D is kerosene.

(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.