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

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

Science: Internal breakup

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)