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The strangth of class decreased every year at 10%. If strangth of class was 70000    2 year ago . Find present strangth.

Posted by Rathi Kajal (Mar 20, 2017 11:02 p.m.) (Question ID: 4279)

  • Answers:
  • Ans. Strength of class 2 years ago = 70000

    Decreasing rate = 10%

    Strength after 1 year = {tex}70000 - {70000\times 10\over 100} = 70000-7000{/tex}

    = 63000

    Present Strength = {tex}63000-{63000\times 10\over 100} = 63000-6300{/tex}


    Answered by Naveen Sharma (Mar 21, 2017 7:09 a.m.)
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What is oscillation


Posted by Vibhash Kumar (Mar 20, 2017 5:10 p.m.) (Question ID: 4217)

  • Answers:
  • Movement of body in its fix axis by the moving object to and frocalled oscillation.

    Answered by Shalini Jha (Mar 20, 2017 7:54 p.m.)
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  • To and fro movement of a body around fixed axis is called oscillation.

    Answered by RAJENDRA SINGH (Mar 20, 2017 5:45 p.m.)
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The products of combustion are :

(a) carbon dioxide and water

(b) Oxygen and water

(c) only carbon dioxide

(d) only oxygen

Posted by Amlan Acharya (Mar 18, 2017 6:29 p.m.) (Question ID: 4065)

  • Answers:
  • a)

    Answered by Mayank Malhotra (Mar 18, 2017 9:23 p.m.)
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Sodium zeolite??


Posted by Harsh Dave (Mar 13, 2017 10:55 a.m.) (Question ID: 3667)

Anti-freeze is a mixture of.


Posted by Harsh Dave (Mar 13, 2017 10:54 a.m.) (Question ID: 3666)

  • Answers:
  • Antifreezes such as ethylene glycol or propylene glycol commonly added to water in automobile cooling systems prevent damage to radiators.

    They are a mixture of alcohols and are water based.

    Answered by Shweta Gulati (Mar 13, 2017 11:42 p.m.)
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What do we call the sudden and extreme changes taking place during the development of an animal

Posted by sabari don (Mar 11, 2017 2:56 p.m.) (Question ID: 3520)

  • Mutations

    Posted by Priyankaa Singh (Mar 11, 2017 6:01 p.m.)
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Why is it necessary to conserve paper? State any two ways in which you xan conserve paper?

Posted by Rathi Kajal (Mar 10, 2017 10:03 p.m.) (Question ID: 3482)

How do city sewage and industrial waste discharged into the rivers become a souece of water pollution?

Posted by Rathi Kajal (Mar 10, 2017 9:54 p.m.) (Question ID: 3481)

How is ozone formed?

Posted by Rathi Kajal (Mar 10, 2017 9:52 p.m.) (Question ID: 3480)

  • Answers:
  • O2=O+O       (by UV rays)

    O2+O=O3 (ozone)

    Answered by Sudhanshu Baranwal (Mar 11, 2017 10:32 a.m.)
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Greater the area of contact, Greater will be the

Posted by Fiza Divekar (Mar 10, 2017 2:51 p.m.) (Question ID: 3430)

  • Answers:
  • Lesser will be the pressure 

    Answered by Rohini Banerjee (Mar 18, 2017 3:53 p.m.)
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Do fruits and vegetables conduct electricity? Explain.

Posted by Rathi Kajal (Mar 09, 2017 6:15 p.m.) (Question ID: 3378)

  • Answers:
  • Not jouce is juice

    Answered by Durgeshmohan Mishra (Mar 14, 2017 4:59 p.m.)
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  • Yes because i they connected by zinc and copper plate because of their jouce

    Answered by jaya dhakate (Mar 09, 2017 6:32 p.m.)
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When do you replace a bulb with a light emitting diode?

Posted by Rathi Kajal (Mar 09, 2017 6:14 p.m.) (Question ID: 3377)

what is adolescence


Posted by Adarsh Bhaskar (Mar 08, 2017 1:16 p.m.) (Question ID: 3295)

  • Answers:
  • Generally, this period is referred as teenage. During this period, the younger boy/ girl emerges from childhood and merges into adulthood.  In fact it is  an age of great changes. Like physical growth, changes in emotions, etc.

    Answered by Sita Kadian (Mar 08, 2017 1:24 p.m.)
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when  does  a girl reaches adolescence


Posted by Varma Ganesh Coimbatore (Mar 07, 2017 5:58 p.m.) (Question ID: 3246)

  • Answers:
  • Upto 14-15

    Answered by Shally Sunekha (Mar 07, 2017 6:26 p.m.)
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Define smoge

Posted by Shyamlal Prajapat (Mar 05, 2017 4:39 p.m.) (Question ID: 3114)

  • Answers:
  • Smoke+fog

    Answered by Pastel Grudge (Mar 05, 2017 9:05 p.m.)
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Name some gases that polluted atmosphere 

Posted by Shyamlal Prajapat (Mar 05, 2017 4:35 p.m.) (Question ID: 3113)

  • Where is answer



    Posted by Shyamlal Prajapat (Mar 05, 2017 4:37 p.m.)
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  • Answers:
  • The gases like cfcs pollute atmospere

    Answered by Kritika Jain (Mar 15, 2017 8:35 p.m.)
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List some ways to reduce air and water pollution 

Posted by Shyamlal Prajapat (Mar 05, 2017 4:33 p.m.) (Question ID: 3112)

  • Answers:

    - to use ecofriendly means of transportation preferably bicycles or walking till possible

    - to stop people smoking which releases smokes and thus causes various health diseases


    -not to throw waste in rivers etc

    -  Self hygiene must be maintained and drinking water must not be polluted.

    {for more ways google it}


    Answered by JAHANVI MALHOTRA (Mar 05, 2017 7:52 p.m.)
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Define the range of vision

Posted by bn kumar (Mar 03, 2017 7:05 p.m.) (Question ID: 2992)

  • Answers:
  • the distance between far point and near point of an eye is called range of vision

    for a normal adult eye range of vision is 25cm-infinity

    Answered by Khushi Koshta (Mar 03, 2017 7:08 p.m.)
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What's the difference between  foetus and the embryo.


Posted by Pratibha Bhatia (Mar 02, 2017 4:53 p.m.) (Question ID: 2912)

  • Answers:
  • When speaking of human development, the term embryo refers to the first eight weeks of pregnancy, while foetus refers to the later stages of pregnancy after eight weeks. 

    The embryonic period is all about the formation of important systems of the body. 

    The foetal period, on the other hand, is more about growth and development so the baby can survive in the outside world.

    Answered by Shweta Gulati (Mar 03, 2017 2:40 a.m.)
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what are the difference betwwen comets and planets?

Posted by janmejay Bhardwaj (Mar 01, 2017 6:57 p.m.) (Question ID: 2876)

  • Answers:
    1. Comets are substance made up of ice and dust and planets are spherical bodies that revolve around the sun.
    2. Ex of comets is Hiliary  comet and Ex of planet is Earth


    Answered by Pratibha Bhatia (Mar 01, 2017 9:37 p.m.)
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How can we find the calorific value of a fuel

Posted by Vidushee Sharma (Mar 01, 2017 1:10 p.m.) (Question ID: 2858)

  • Answers:
  • Ans. Calorific value of a fuel can be determined using Bomb Calorimeter. The procedure is explained below.

    The crucible of the calorimeter is filled with the known mass of fuel, and then it is ignited. This heats the surrounding water, and the initial and final temperatures are recorded using a thermometer. The calorific value can be determined using the heat balance. 
    Heat given by the fuel is equal to the heat gained by the water.

    Answered by Naveen Sharma (Mar 01, 2017 1:39 p.m.)
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Explain the role played by nutrition during adolescence.

Posted by Rathi Kajal (Feb 25, 2017 5:25 p.m.) (Question ID: 2651)

  • Answers:
  • Nutrient needs are greater during adolescence than any other time in the lifecycle. Between the ages of 12 and 18, older children will experience several growing spurts, which are associated with hormonal, intellectual, and emotional changes that can make adolescence a challenging part of life. Failure to consume an adequate diet at this time can result in delayed physical development and growth. Nutrition is also important during this time to help prevent adult diet-related chronic diseases, such as cardiovascular disease, cancer, diabetes, and osteoporosis.

    Answered by Shweta Gulati (Feb 26, 2017 1:50 p.m.)
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How are the changes which take place at puberty regulated?

Posted by Rathi Kajal (Feb 25, 2017 4:40 p.m.) (Question ID: 2640)

  • Answers:
  • changes during the age of  puberty are regulated by the testosterone in male and by estrogen and progesterone in female.

    Answered by Pratibha Bhatia (Mar 01, 2017 9:40 p.m.)
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why is installing a water purifier that only removes odour and dirt is not enough

Posted by Deepak Somasekar (Feb 22, 2017 8:34 p.m.) (Question ID: 2473)

what is the difference between sound wave and light wave ?

Posted by Krati Chaturvedi (Feb 17, 2017 8:54 p.m.) (Question ID: 2266)

  • Answers:
  • The difference between Sound waves and Light Waves are: Sound Waves require a medium where Light Waves do not require a medium

    <h3>Sound Waves</h3>

    1. Require a medium.

    2. Travel with a speed of 332 m/s at 0 C.

    3. Are longitudinal waves consisting of compressions and rarefactions.

    4. Are of different frequencies, giving notes of different pitches.

    5. Do not travel far as their energy is dissipated easily.

    <h3>Light Waves</h3>

    1. Do not require a medium

    2. Travel with a speed of 3 *10m/s.

    3. Are electromagnetic waves consisting of varying electric and magnetic fields.

    4. Are of different frequencies, resulting in different colors.

    5. Can travel through a much greater distance.

    Answered by imran khan (Feb 17, 2017 9:54 p.m.)
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Can anyone provide me some analytical questions for the chapter Air and Water pollution ?

Posted by Akanksha Arora (Feb 11, 2017 3:19 p.m.) (Question ID: 2014)

  • Answers:
  • Question 1:

    What are the different ways in which water gets contaminated?

    Answer :

    Water gets contaminated by the addition of:
    (i) Agricultural chemicals: Farmers use excessive amounts of pesticides and fertilizers to increase crop production. These chemicals get carried away to the water bodies due to rains and floods which lead to water pollution.
    (ii) Industrial wastes: Industries release harmful chemical wastes into water sources, thereby polluting them.
    (iii) Sewage wastes: Waste materials from kitchens, toilets, and laundry sources are also responsible for contaminating water.

    <h1> </h1>

    Question 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.
    (v) Controlling the emissions from vehicles and household chimneys.

    Question 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. Purification can be done by water purifying systems or by boiling the water.

    Question 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.


    Question 5:

    Explain the differences between pure air and polluted air.

    Answer :

    Pure air contains around 78% nitrogen, 21% oxygen, and 0.03% carbon dioxide. Other gases such as argon, methane, ozone, and water vapours are also present in small quantities. When this composition of air is altered by the addition of harmful substances or gases such as nitrogen dioxide, sulphur dioxide, carbon monoxide, and particulate matter, then the air is said to be polluted.

    Question 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.

    Question 7:

    Which of the following is not a greenhouse gas?
    (a) Carbon dioxide
    (b) Sulphur dioxide
    (c) Methane
    (d) Nitrogen

    Answer :

    (d) Nitrogen


    Question 8:

    Describe the ‘Greenhouse Effect’ in your own words.

    Answer :

    Greenhouse effect may lead to global warming, i.e., an overall increase in the average temperature of the Earth. Greenhouse effect is caused by greenhouse gases. Examples of greenhouse gases include carbon dioxide, methane, and water vapour. When solar radiations reach the Earth, some of these radiations are absorbed by earth and then released back to the atmosphere. Greenhouse gases present in the atmosphere trap these radiations and do not allow heat to leave. This helps in keeping our planet warm and thus, helps in human survival. However, an indiscriminate increase in the amount of greenhouse gases can lead to excessive increase in the Earth’s temperature leading to global warming.

    <h1> </h1>

    Question 9:

    Prepare a brief speech on global warming. You have to deliver the speech in your class.

    Answer :

    Global warming is an increase in the average temperature of the Earth’s surface. It occurs as a result of an increased concentration of greenhouse gases in the atmosphere. The greenhouse gases include carbon dioxide, methane, and water vapour. These gases trap solar radiations released back by the Earth. This helps in keeping our planet warm and thus, helps in human survival. However, an increase in the amount of greenhouse gases can lead to an increase in the Earth’s temperature leading to global warming.

    Question 10:

    Describe the threat to the beauty of the Taj Mahal.

    Answer :

    Acid rain is a major threat to the beauty of the Taj Mahal. When acid rains fall on the monument (that is completely made of marble), they react with marble to form a powder-like substance that is then washed away by the rain. This phenomenon is known as marble cancer. Also, the soot particles emitted from the Mathura oil refinery located near Agra is leading to the yellowing of the marble. 

    Question 11:

    Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

    Answered by imran khan (Feb 11, 2017 3:28 p.m.)
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Mercury has day in one part and night in other part.Give reason?

Posted by Nageswara Rao (Feb 09, 2017 2:39 p.m.) (Question ID: 1949)

  • plz answer its my hw.......i am not able to ans..:(


    Posted by Nageswara Rao (Feb 09, 2017 2:51 p.m.)
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  • Answers:

    On Mercury temperatures can get as hot as 430 degrees Celsius during the day and as cold as -180 degrees Celsius at night.
    Mercury is the planet in our solar system that sits closest to the sun. The distance between Mercury and the sun ranges from 46 million kilometers to 69.8 million kilometers. The earth sits at a comfy 150 million kilometers. This is one reason why it gets so hot on Mercury during the day.

    The other reason is that Mercury has a very thin and unstable atmosphere. At a size about a third of the earth and with a mass (what we on earth see as ‘weight’) that is 0.05 times as much as the earth, Mercury just doesn’t have the gravity to keep gases trapped around it, creating an atmosphere. Due to the high temperature, solar winds, and the low gravity (about a third of earth’s gravity), gases keep escaping the planet, quite literally just blowing away.
    Atmospheres can trap heat, that’s why it can still be nice and warm at night here on earth.
    Mercury’s atmosphere is too thin, unstable and close to the sun to make any notable difference in the temperature.

    Space is cold. Space is very cold. So cold in fact, that it can almost reach absolute zero, the point where molecules stop moving (and they always move). In space, the coldest temperature you can get is 2.7 Kelvin, about -270 degrees Celsius.
    Sunlight reflected from other planets and moons, gases that move through space, the very thin atmosphere and the surface of Mercury itself are the main reasons that temperatures on Mercury don’t get lower than about -180 °C at night

    Answered by imran khan (Feb 09, 2017 8:22 p.m.)
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Why water comes only on our earth and not comes on other planets?



Posted by Abhishek Kumar (Feb 08, 2017 9:37 p.m.) (Question ID: 1928)

  • Answers:
  • The water that makes Earth a majestic blue marble was here from the time of our planet's birth, according to a <a href="">new study of ancient meteorites</a>, scientists reported Thursday.

    Where do the oceans come from? The study headed by <a href="">Adam Sarafian</a> of the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts, found that our seas may have arrived much earlier on our planet than previously thought.

    The study pushes back the clock on the origin of Earth's water by hundreds of millions of years, to around 4.6 billion years ago, when all the worlds of the inner solar system were still forming.

    Scientists had suspected that our planet formed dry, with high-energy impacts creating a molten surface on the infant Earth. Water came much later, went the thinking, thanks to collisions with wet comets and asteroids.

    "Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space," said study co-author <a href="">Horst Marschall</a>, a geologist at WHOI.

    For that reason, he said, scientists thought that "surface water as it exists on our planet today must have come much, much later—hundreds of millions of years later."

    Answered by imran khan (Feb 09, 2017 8:25 p.m.)
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What happens when reflection by a plane, polished surface is 

Posted by Praveen Chetalla (Jan 28, 2017 7:03 p.m.) (Question ID: 1654)

  • Answers:
  • When a rays of light reflected by a plane mirror image formation takes place.


    Answered by RAJENDRA SINGH (Jan 28, 2017 7:40 p.m.)
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What is bitumen?


Posted by Irfan Alam (Jan 27, 2017 5:08 p.m.) (Question ID: 1633)

  • Answers:
  • Ans. Bitumen is a mixture of Organic Liquids that are highly Viscous, Black, Sticky, Entirely Soluble in Carbon Disulfide, and composed primarily of highly condensed Polycyclic Aromatic Hydrocarbons.

    Naturally occurring or crude bitumen is a sticky, tar-like form of petroleum which is so thick and heavy that it must be heated or diluted before it will flow. At room temperature, it is much like cold molasses.

    Answered by Naveen Sharma (Jan 27, 2017 5:23 p.m.)
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