[Answerkey] Science MCQs of UPSC CPF/CAPF 2012 with explanation for all booklets (a,b,c,d)

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  1. Science: Internal Breakup
  2. Science: Theory based (Static)
  3. Science: Current Affairs based (aka Science-Tech)

Science: Internal breakup

Theory based12
Current affairs based4
Total (science) out of 12516

Science: Theory based (Static)

1. When an iron nail is dipped in a solution of copper sulphate, the iron nail becomes brownish in colour and the blue colour of copper sulphate solution fades after some time. The reaction is an example of chemical
(a) combination
(b) decomposition
(c) displacement
(d) double displacement
This Is Displacement Reaction. Chapter 1 of NCERT Science Class 10
Answer is (C)
2. Bleaching powder is added in water used for drinking purpose. The role of bleaching powder in this case is

  1. of disinfectant
  2. of bleaching agent
  3. to remove impurity
  4. to decrease the pH

It is used for disinfecting drinking water to make it free of germs. Chapter 2 of NCERT Science Class 10.
Answer is (A)
3. If four balloons A, B, C and D are filled with hydrogen, oxygen, helium and nitrogen gases respectively and left in air, which balloon reaches to the highest distance from the Earth?

  1. Balloon A
  2. Balloon B
  3. Balloon C
  4. Balloon D

Hydrogen lighest, helium second lightest.  So Ballon (A) will reach highest.
Answer (A)
4. Which one among the following salts causes hardness to the water?

  1. Calcium bicarbonate
  2. Calcium carbonate
  3. Sodium sulphate
  4. Potassium chloride
  • Sodium carbonate (washing soda) is used for removing permanent hardness of water. (NCERT CLASS 10, SCIENCE CHAPTER 2) So (B) is incorrect.
  • Presence of calcium and magnesium salts in the form of hydrogencarbonate (also known as bi-carbonate), chloride and sulphate in water makes water ‘hard’. (NCERT CLASS 11 CHEMISTRY, CHAPTER 9)

So (A) is the answer.
5. Which among the following causes stomach pain in human body?

  1. base
  2. acid
  3. salt
  4. bacterium

well if you swallow concetrated sodium hydroxide (Base) or Sulfuric Acid (Acid), It is also going to cause stomach pain. Besides there are many bacteria, good for stomach and digestion.
They should have set the options a bit more clearer.
Anyways, given the situation (D) seems to be the appropriate answer.
6. Byssinosis disease is common in workers of

  1. rubber industry
  2. ceramic industry
  3. textile industry
  4. iron and steel industry

Byssinosis, a lung disease that affects the cotton ginning workers. So (C) is the answer.
7. A television remote uses

  1. infrared waves
  2. cosmic waves
  3. microwaves
  4. ether waves

NCERT Class 12 Physics “GaAs (Eg~ 1.4 eV) is used for making infrared LED. These LEDs find extensive use in remote controls, burglar alarm systems, optical communication, etc.”
So, (A) is the answer.
8. A microwave oven uses wave with a

  1. large wavelength in the invisible range
  2. small wavelength in the visible range
  3. large wavelength in the visible range
  4. small wavelength in the invisible range

visible light=10^(-6) meter wavelenght
Microwave=invisible light, 10^-1 to 10^-3 meter wavelenght.
(NCERT PHYSICS CLASS 12, CHAPTER 8)
Thus, Compared to visible light, microwaves have longer wavelengths and are therefore invisible to the human eye. Therefore (A) is the answer.
9. Use of tamarind juice as a part of our meal helps

  1. to prevent tooth decay
  2. to take care of excess fluoride in drinking water
  3. for easy digestion of food
  4. to increase the strength of bones

Tamarind is used in Ayurvedic medicine for gastric and/or digestion problems (wiki)
Answer (C)
10. Wi-Fi in a computer implies

  1. wired local area network
  2. wireless local area network
  3. high fidelity
  4. high efficiency

Wi-fi Is a term used to describe wireless local area network (WLAN) products so (B) is the answer.
11. A thin pin of iron can be made to float on water (drinking) in a bowl. This phenomenon is due to the

  1. surface tension of water
  2. viscous nature of water
  3. presence of ionic bonds in water molecules
  4. presence of covalent bonds in water molecules.

It is because of Surface tension. Answer is (A)
12. To start your loaded trolley bag, you exert more force than when it is moving. This is an example of

  1. first law of thermodynamics
  2. second law of thermodynamics
  3. Newton’s second law of motion
  4. Newton’s first law of motion.

This is because of Newton’s First law. Every object continues to be in its state of rest or uniform motion ins a straight line, if no net forces acts upon it.
Answer is (D)

Science: Current Affairs based (aka Science-Tech)

1. Consider the following statements about the ‘Curiosity’ rover

  1. It is a robotic mission for exploration of the Mars launched by NASA.
  2. It is powered by solar energy

Which of the statements given above is/are correct?

  1. 1 only
  2. 2 only
  3. Both 1 and 2
  4. Neither 1 nor 2

Statement 1 is true.
Statement 2 is false because this rover is powered by nuclear energy.
Answer (A)
2. Consider the following statements :

  1. Discovery of Higgs boson of which scientists are almost certain may discard Einstein’s special theory of relativity.
  2. Probable discovery of a particle which moves faster than light may prove Stephen Hawking wrong.
  3. Probable discovery of a particle that moves faster than light may go against Einstein’s special theory of relativity.

Which of the statements given above is/are correct?

  1. 1 and 2
  2. 1 only
  3. 3 only
  4. 1 and 3

Einstein had said, nothing can travel faster than light. So if such particle is found, then it’ll go against Einstein’s So, statement 3 is correct. (neutrino topic)
Discovery of Higgs Boson will actually agument Einstein’s special theory of relativity. Therefore statement 1 is wrong and all options containing statement 1 are wrong.
We are left with answer (C).
http://weeklyworldnews.com/headlines/41410/god-particle-found-in-new-jersey/
second approach:
Einstein’s special theory says time travel is not possible, some believe Higgs Boson will make time-travel possible. From that angle, some would answer (D). However other scientists say Higgs Boson will not make time-travel impossible.
3. In most of the children’s toys- a toxic chemical remains present. In this respect, which among the following statements is/are correct?

  1. The name of the toxic element is phthalates which are esters of phthalic acid.
  2. They are mainly used as plasticizers, i.e., substances added to plastics to increase their flexibility and longevity.
  3. They are easily released into environment because there is no covalent bond between the phthalates and plastics in which they are mixed
  1. Only 1
  2. 1, 2
  3. 2, 3
  4. 1, 2 and 3
  1. They’re esters of are esters of phthalic acid. So 1 is correct. (wiki)
  2. Phthalates are primarily used in toys to soften the polyvinyl chloride of plastic toys and make them supple and chewy for babies. They are a cheap alternative to the non-phthalate softeners used in the West. So 2 is correct. www.in.news.yahoo.com/trouble-toys-000000055.html
  3. Phthalates are easily released into the environment because there is no covalent bond between the phthalates and plastics in which they are mixed. So 3 is also correct. http://www.niehs.nih.gov/research/supported/sep/2009/phthalate/index.cfm

Answer is D
4. In the recent past, a fundamental particle has been claimed to be experimentally observed, at a European Laboratory in Geneva, to travel at a speed greater than that of light in vacuum. The name of the particle is

  1. electron
  2. positron
  3. neutron
  4. neutrino

It was Neutrino however, later it was found the CERN experiment was faulty and neutrinos donot travel faster than light.
Anyways, Answer is (D)

[Answerkey] Science MCQs of UPSC CPF/CAPF 2012 with explanation for all booklets (a,b,c,d)




So far 50 Comments posted

  1. Nirmal

    With regard to question on stomach pain we drink COKE which has pH 2.5,clearly acidic so to say that we have stomach pain after acid is not reasonable ,please correct me if i am wrong.

  2. Nirmal

    we generally came across term ‘acidity’ while complaining about stomach pain so does’nt be more suitable to answer base as answer as commonly used ‘ENO’ is antaacid.

  3. Nirmal

    i am copy pasting it from a website:
    About Eno and how it works

    This medicine helps relieves the symptoms and discomfort caused by excess acidity such as indigestion, nausea and flatulence.

    This medicine belongs to the class of medicines called antacids. It works by neutralising excess acid which protects the stomach and also helps relieve symptoms of indigestion. It also helps release trapped wind which is expelled during belching or burping.

    This medicine is available in the form of a powder which has to be dissolved in water before taking.

  4. Dharm Veer Sukhwal

    Why you of all people said Helium is the lightest gas…..What has Hydrogen done to you to loose its credit of being the lightest gas

    1. Nirmal

      I agree hydrogen does not have have neutrons (which has biggest share in mass) and helium contains 2 neutrons(atomic no:2) so it unreasonable to call helium lighest

  5. Ashok

    Sir Please Guide me and reply..Sir i have qualify the Following Exam-
    SSC FCI Assistant Grade III 2012 Selected
    SBI Assistant Selected
    SSC CGL 2012 Called For Interview and will definetly get non-intervew CAG Audiotr.
    IBPS PO-2 Qualify Marks- 176 and can get selected Final Selection but After jan.
    IBPS RRB PO- Marks-135 Also can get selected.
    Sir Please suggest what should better so that i can do my civil services Preparation with Job or Should i leave all and prepare for Civil.
    Pls Reply

    1. Mrunal

      Workload and stress level is quite heavy for bank jobs, particularly PO.
      So, if your ultimate aim is get a job for preparing UPSC, better check workload details of those SSC jobs (particularly CAG auditor).

    2. nilotpal

      go for bank job and take leave without pay…that is education leave and then prepare for civil services.

  6. sakthi

    Pardon me but isn’t hydrogen gas lighter than helium? Helium is only used because hydrogen is inflammable.

  7. Srinu

    Hi mrunal, Can u clarify hydrogen vs helium issue? which is lighter and why?
    Many sources say hydrogen is lighter!

  8. Anshuman Rai

    During bachpan when I used to visit balloon feriwala, he gave me the balloon and perhaps said it contains helium, I remember those words.

    1. Titus

      Yes Balloons are Filled with Helium ,Eventhough Hydrogen is Lightest its Highly Inflammable So Helium is Used to Avoid Accidents ,But for Our Question hope ” Hydrogen” Will be the Right Answer

    1. N/A

      But, there is no option like both 1 and 3. Moreover, the purpose is for “drinking water”. Hence, in my opinion, the answer (a) disinfectant is correct. No doubt..

  9. Praveen Kumar

    Hi Mrunal,

    Please change answer for the following question :
    12. To start your loaded trolley bag, you exert more force than when it is moving. This is an example of

    first law of thermodynamics
    second law of thermodynamics
    Newton’s second law of motion
    Newton’s first law of motion.
    This is because of Newton’s First law. Every object continues to be in its state of rest or uniform motion ins a straight line, if no net forces acts upon it.
    Answer is (D)

    Here answer will be (C) because force is product of mass and acceleration. Where acceleration is change of velocity per unit time. If we apply Newton’s first law, then there is no force applicable whether body is in motion( as constant velocity) or body is static. Force is zero in both the case.
    Now question asked why there is more force applied to static object as compared to moving object. Therefore, force cannot be zero, they must be different. And the moment different force comes, immediately second law and third law come into picture.
    Otherwise put this question as ambiguous for safer side.

    1. Nirmal

      THE ANSWER MUST BE (D) BECAUSE IT IS ALSO CALLED ‘LAW OF INERTIA’ .MORE FORCE IS REQUIRED TO CHANGE ITS STATE OF INERTIA (IT RESIST ANY CHANGE) OF REST THAN THAT OF INERTIA OF MOTION

  10. Sumiran kumar

    Dear Mrunal i think that for question number 12 answer should be
    Ans Newton second law of motion
    1. First law state that a body in rest will be in rest or a body in motion will be in motion untill unless some external force is applied.
    2. Second law states that rate of change of momentum is directly proportional to the external force applied
    Now in this case initially when there is a big chnge in momentum that means u haveto apply greater force while once it starts moving the force decreases as the rate of chnge of momentum is not substantial.
    I would appreciate your valuable suggestion.

  11. nilotpal

    sir the question about hydrogen and helium gas balloon for which one will go at greater altitude ,it is true that hydrogen is the lighter than helium but a balloon filled with hydrogen will not go at higher altitude because hydrogen is highly inflamable ,so the balloon filled with hydrogen will not go much higher as compared to helium balloon.

  12. Sumiran kumar

    Nilotpal
    What the inflamibility has to do with higher latitude inside the baloon there is nthng to initiate burning afterall….

    1. nilotpal

      cant u consider about density factor which seriously decreases as we go at higher altitudes which favours the hydrogen balloon, if ur balloon is not going to survive at higher altitude what is the point in considering its light weight ,dear there is another factor and that is ofcourse electric charges present in higher layer of atmosphere. So ,now i think it is clear for u.u can chek the answer on several website which compare helium and hydrogen balloons.

      1. Nirmal

        don’t take so many factors(remember it is general test not a IIT paper!) it was simple question based simply on density .

        1. nilotpal

          yes my dear friend if u consider the exam a sipahi bharti exam then u are right plz excuse me for considering upsc exams equivalent to IITs.(lol)

          1. Nirmal

            THE CRUX OF WHAT I AM SAYING IS UPSC EXAM IS GIVEN BY ALL ASPIRANTS REGARDLESS OF ANY STREAM. IT IS VERY GENERAL IN APPROACH NOT A SPECIALIST LIKE IIT .I HOPE YOU WILL GET MY POINT .BY THE WAY EXCUSE ME ,I AM NOT COMPAIRING IIT AND UPSC .I AM JUST POINTING TO A BASIC FLAW IN YOUR ARGUMENT (ELECTRIC CHARGE IN ATMOSPHERE,HOW CAN A PERSON NON SCIENCE BACKGROUND CAN ACCOMODATE THESE CONCEPTS)

          2. Nirmal

            ONE IMPORTANT MORE YOU HAVE TOLD DENSITY DECREASES WITH ATMOSPHERE OK NOW IF WE STILL COMPARE DENSITIES OF HYDROGEN AND HELIUM THEN HYDROGEN WILL HAVE LOWER DENSITY COMPARED TO HELIUM (WHY?:BECAUSE OF AVAGADRO LAW).THEREFOR HYDROGEN WILL RISE FURTHER DUE TO LOW DENSITY.

  13. ashok kumar

    bacteria is reson for stomach pain….it correct because acid produce only burning sensation its not a pain

  14. Khumukcham Napoleon

    sir, ‘curiosity’ is the name of the mission or the name of the robot. i have choosen option d as i hope it is the name of the robot not the mission.

  15. ANUPA PATEL

    SIR,
    I am in confusion in some qsn which doesn’t provided any type of reason for particular answers.

  16. amrutha

    for the balloon to move faster,what is important is not the weight of the air inside it(it will have minimal effect) what is important is the
    the air weight which causes the flotation, equivalent to the weight of the air that would be in a balloon full of air. Air is made of mostly nitrogen(molecular)weight 28g per 24 liters at room temperature.
    in figures, a 24 liter helium balloon weighs 4g and that means it displaces 28 minus 4 that is 24g in air where as per hydrogen as it exists as diatomic,a 24 liter hydrogen balloon weighs 2g and can displace 28 minus 2 that is 26g in air.so u pick.
    so,even though hydrogen is lighter than helium gas, helium filled balloons move faster so answer is c

    1. HYDROGEN BALOON

      WITH DUE REGARD MAM I JUST WANT TO SAY THAT QUESTION IS ABOUT WHICH WILL TRAVEL MORE DISTANCE NOT WHICH WILL MOVE FASTER !

    2. THE SERIOUS PLAYER

      MAM I THINK YOU HAVE GOT RIGHT ANSWER FROM HELIUM BALOON (OMG! BALOON IS JUSTIFYING HIMSELF)HE HIMSELF CONFESSES THAT HYDROGEN IS RIGHT!!!!!JUST SEE BELOW (HELIUM IS STILL BELOW)

  17. helium BALOON

    Yes mam hydrogen baloon is slow but he travel more distance than me(THE MIGHTY HELIUM BALOON)

  18. shashi bhushan

    no dout hydrozen is lightest gas but i think helium. because above side of atmosfier hydrozen react with oxigen . and its resultant it does not filled up airoplane tyre etc.

  19. shashi bhushan

    Use of tamarind juice i think its contantain vitamin c and basically use to prevent teeth problem

  20. Rahul

    Answer of question number 12 will be Newton’s first law of motion.
    A simple example of this would be falling of coin the glass experiment …I have studied this in class 7…So all of you would have studied the same.

  21. Anuraag k

    I m getting smwhere arnd 53 correct in capf 2012..i attempted 78..cn u plz guide me what are my chances of passing this exam

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