1. Science: CDS, CAPF, CSAT
    1. Science MCQs: toughness/ difficulty level
    2. Science reference booklist for next CDS exam
  2. Physics Answerkey (9 MCQs)
    1. Heat (2)
    2. Motion (2)
    3. Optics (2)
    4. Electricity (2)
    5. Astro (1)
  3. Chemistry Answerkey (5 MCQs)
  4. Biology Answerkey (12 MCQs)
    1. Botany (3)
    2. Zoology(1)
    3. Disease/microbes (2)
    4. Human Biology(6)

Science Analysis: CDS, CAPF, CSAT exam

Now its time for

CDS 2014 answerkery-Science internal breakup

Science Topic CDS1-2014 CDS2-2013 CDS1-2013 CAPF-2013 CSAT-2013
Science 26 23 28 20 13
total MCQs 120 120 120 125 100
% 22% 19% 23% 16% 13%
  • Science portion has remained more or less the same ~20% in last three CDS exams.
  • In CAPF, science is bit lower because they’ve to make room for Aptitude also.
  • In CSAT, science is bit lower because they’ve to make room for Environment-Biodiversity and Economy. (In CDS they don’t ask much Economy).

PS: I’ve not counted Environment-Biodiversity and Defense related MCQs here. because for the purpose of CDS strategy, one should observe them as ‘separate’ categories. this article is confined only to the traditional physics, chemistry, biology.

Internal breakup: Science in CDS-(I)-2014

Physics 9
Chemistry 5
Biology 12
Total 26

Science-tech (Current affairs type MCQ) are curiously absent. [I count defence MCQs- as a separate category for CDS). Chemistry got bare minimum attention – this is same as CSAT pattern.

Science MCQs: toughness/ difficulty level

Debatable. Depends on person to person, depending on his preparation level.

NCERT class Science MCQs in CDS 1 -2014
upto 10 12
11, 12 8
total out of 26 20 = more than 75%

You can see, majority of the MCQs were from NCERT. But the challenge: many don’t prepare class 11-12 science in detail. That’s why paper may look tough. Anyways, following is the list of tough MCQs (in my opinion) because Information not given straight forward in NCERT or other usual books (Lucent GK Book, GS Manual etc.)

  • mobile charger is step down inverter
  • black hole’s event horizon
  • mirror (although given in class 10 NCERT but most just skip mugging up this table)
  • why ethylene di-bromide added to petrol
  • Marchintia
  • Fats
  • Amnion
  • Anorexia nervosa (asked from Class 12 psychology book- which most players don’t read.)

Anyways, let’s start:

Science reference booklist for next CDS exam

  1. Since 20 out 26 can be directly solved through NCERTs. so NCERTs become the obvious choice. But you should study of Class 11 and 12 as well- ignoring formulas, but focusing on principles/concepts/GK. (Advice applies to CSAT aspirants as well. This Class11/12 seems to be the new BackbreakingTM move upcoming for CSAT 2014.)
  2. For additional reading you may consult Lucent GK Book Or GS Manual (although doesn’t seem really necessary for the science section, the way things have rolled in this CDS paper, and even in the last CSAT.)
  3. Do solve the old papersets of CDS and UPSC Civil service preliminary exams.

NCERT Download links:

NCERT Class 7 to 10:

Topicwise classified and uploaded: Mrunal.org/Download (upto class 10).
For Class11- 12 either download from NCERT’s official site, or wait for few days till I classify it.
**for mental disorders/appendix. Because UPSC did ask one question from here.

Physics Answerkey (9 MCQs)

Internal breakup

Heat 2
Motion 2
Optics 2
Electricity 2
Astro 1
Total 9

Heat (2)

Q1. Two layers of a cloth of equal thickness provide warmer covering than -a single layer of cloth with doable the thickness. Why?

  1. Because of the air encapsulated between two layers
  2. Since effective thickness of two layers is more
  3. Fabric of the cloth plays the role
  4. Weaving of the cloth plays the role

NCERT Class 7 Ch 4 Page 10

Suppose you are given the choice in winter of using either one thick blanket or two thin blankets joined together. What would you choose and why? Remember that there would be a layer of air in between the blankets… This air prevents the flow of heat from our body to the cold surroundings. So, we feel warm.

Hence answer A

Q2. A metal screw-top on a glass bottle which appears to be stuck could be opened by using the fact that

  1. the metal expands more than the glass when both are heated
  2. the metal and glass expand identically when heated
  3. the metal shrinks when heated
  4. both metal and glass shrink when cooled

NCERT physics, Class 11 Ch 11, Page 4

It is our common experience that most substances expand on heating and contract on cooling. A change in the temperature of a body causes change in its dimensions. The increase in the dimensions of a body due to the increase in its temperature is called thermal expansion. Thermal expansion coefficients given in Table 11.1

Glass : 0.32. And all the metals have higher coefficient than glass. Therefore, (A) is the explaination.

Georgia State University confirms

Even if you heated the metal lid and the glass jar equally, you would loosen the lid a bit because the thermal expansion coefficient of the metal is greater than that of the glass.

Hence answer (A)

Motion (2)

Q1. You are asked to jog in a circular track of radius 35 metres. Right at one complete round on the circular track, your displacement and the distance covered by you are respectively

  1. zero and 220 metres
  2. 220 metres and zero
  3. zero and 110 metres
  4. 110 metres and 220 metres

NCERT 9 Ch 8 Page 2

Displacement: If final position coincides with the initial position, then displacement is zero.

Distance=circumference of the circle= 2 (pie)R= 2* (22/7) * 35= 220 metres

Hence answer (A)

Q2. In cricket match, while catching a fast-moving ball, a fielder in the ground gradually pulls his hands backwards with the moving ball to reduce the velocity to zero. The act represents

  1. Newton’s first law of motion
  2. Newton’s second law of motion
  3. Newton’s third law of motion
  4. law of conservation of energy

NCERT Class 11 Ch.5 page 5

Newton’s second law of motion:

A seasoned cricketer catches a cricket ball coming in with great speed far more easily than a novice, who can hurt his hands in the act. One reason is that the cricketer allows a longer time for his hands to stop the ball.  As you may have noticed, he draws in the hands backward in the act of catching the ball

Hence answer (B)

Optics (2)

Q1.No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be

  1. Either plane or convex
  2. Plane only
  3. Concave
  4. Convex only

NCERT 10, Ch 10 page 2

  • page 2: Image formed by a plane mirror is always virtual and erect.
  • page 9: Convex mirrors are preferred because they always give an erect image.

Source#2: Page 441 Lucent GK Book GK.

Q2. The position, relative size and nature of the image formed by a concave lens for an object placed at infinity are respectively:

  1. at focus, diminished and virtual
  2. at focus, diminished and real
  3. between focus and optical centre, diminished and virtual
  4. between focus and optical centre, magnified and real

NCERT Class 10 Ch 10 Page 20, table 10.5

object position image position size of image nature of image
infinite at focus F1 highly diminished virtual and erect.

Therefore answer (A)

Source #2: TMH General Studies Manual Page 28 under Science section.

Electricity (2)

Q1. A mobile phone charger is

  1. an inverter
  2. a UPS
  3. a step-down transformer

(d)-1 step-up transformer

Physical Processes By Mark Pinsent, Page 103

A step down transfer decreases voltage. Mobile phone charger uses a step down transformer.

Q2. When an incandescent electric bulb glows

  1. the electric energy is completely converted into light energy
  2. the electric energy is partly converted into light energy and partly into heat energy
  3. the light energy is converted into electric energy
  4. the electric energy is converted into magnetic energy

NCERT Class 7 ch14 page 6

An electric bulb is used for light but it also gives heat. This is not desirable. This results in  the  wastage  of  electricity. => Answer (B)

Astro (1)

Q3. A typical black hole is always specified by

  1. a (curvature) singularity
  2. a horizon
  3. either a (curvature) singularity or a horizon
  4. a charge

TheHindu Jan 2014

physicist Stephen Hawking, one of the creators of modern theory on black holes, has now questioned the existence of the phenomenon known as event horizon around them. Mening, so far typical black hole is specified by a “horizon”.

Britannica confirms

Event horizon is the Boundary marking the limits of a black hole.

Nothing that enters a black hole can get out or can be observed from outside the event horizon. Likewise, any radiation generated inside the horizon can never escape beyond it.

hence answer (B)

Chemistry Answerkey (5 MCQs)

Q1. Which of the following solutions will not change the colour of blue litmus paper to red?

  1. Acid solution
  2. Base solution
  3. Common salt solution

Select the correct answer using the code given below.

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

NCERT class 7 ch 5 page 8: Acid turns blue litmus red. Bases turn red litmus blue.

Therefore, anything that is not “Acid”, will not change color of litmus from blue to red. Hence (B) 2 and 3 only.

Source #2: Lucent GK Book Page 481

Q2. Which one of the following gases is supporter of combustion?

  1. Hydrogen
  2. Nitrogen
  3. Carbon dioxide
  4. Oxygen

NCERT 8 ch. 6 page 11: Oxygen (in air) is essential for combustion. Answer (D)

Q3.Date of manufacture of food items fried in oil should be checked before buying because oils become rancid due to

  1. Oxidation.
  2. Reduction.
  3. Hydrogenation.
  4. Decrease in velocity.

NCERT 10 Ch 1 Page 13: When fats and oils are oxidised, they become rancid and their smell and  taste  change. Hence answer (A)

Q4. Iron sheet kept in moist air gets covered with rust. Rust is

  1. an element
  2. a compound
  3. a mixture of iron and dust
  4. a mixture of iron, oxygen and water

NCERT Class 12 chemistry Ch3 Page 28-29

Corrosion of  iron  (commonly  known  as  rusting) occurs in presence of water and air.

Rust is the hydrated ferric oxide Fe2O3xH20

Hence answer (D)

counter view: rust is a compound and not a mixture hence answer (B).

Q5.Addition of ethylene dibormide to petrol

  1. Increases the octane number of fuel
  2. Helps elimination of lead oxide
  3. Removes the sulphur compound in petrol
  4. Serves as a substitute of tetra-ethyl lead

Analytical Chemistry VK Sharma, Page A70

Lead oxide deposit is harmful to engine life. Thus, a small amount of ethylene dibromide is also added to petrol for simultaneously removal of lead oxide.

Hence answer (B)

Biology Answerkey (12 MCQs)

internal breakup

Botany 3
Zoology 1
Microbes/Disease 2
Humans 6

Botany (3)

Q1. Which of the following structures of a plant is responsible for transpiration? –

  1. Xylem
  2. Root
  3. Stomata
  4. Bark

Ans. NCERT Class 7 Ch 11 page 129

The water evaporates through the stomata present on the surface of the leaves by the process of transpiration. Answer C

Q2. Which of the following does not possess a specialized conducting tissue for transport of water and other substances in plants?

  1. Marchantia
  2. Marsilea
  3. Cycas
  4. Fern

NCERT Biology class 11, Ch3, Page 8

Pteridophytes include horsetails and ferns. Evolutionarily, they are the first terrestrial plants to possess vascular tissues – xylem and phloem. => D eliminated.

And this also hints that any plant “Before” pteridophtes, doesn’t possess specialized tissues.

Same chapter, page7

The liverworts grow usually in moist, shady habitats such as banks of streams, marshy ground, damp soil, bark of trees and deep in the woods. The plant body of a liverwort is thalloid, e.g., Marchantia.

Hence answer should be (A).

Just to crosscheck, Britannica also confirms:

Vascular plants are those that possess a specialized conducting system for the transport of water, minerals, and food materials, as opposed to the more primitive bryophytes—mosses and liverworts—which lack such a system.

and since Marchantia is one type of liverwort=> it lacks the specialized tissues to transport water etc.

Therefore, answer (A)

Q3. Which one of the following elements is present in green pigment of leaf?

  1. Magnesium
  2. Phosphorus
  3. Iron
  4. Calcium

NCERT biology class 11, Ch12, Page4: Magnesium is a constituent of the ring  structure  of  chlorophyll.

And we know that chlorophyll=green pigment. Hence answer (A)


Q1. Among the following animals, choose the one having three pairs of legs.

  1. Spider
  2. Scorpion
  3. Bug
  4. Mite

NCERT Class 11 Ch1 Page8

Insects represent a group of organisms sharing common features like three pairs of jointed legs. Therefore, answer (C)

Source #2: Lucent GK Book Page 539: there are six feet and four wings in the insects (six feet = three pairs).

Source #3: TMH General Studies Manual, page 87

Just to cross check:

  1. Britannica page on Arachnid: Spiders, Scorpions and Mites fall under “Arachnid” class. and from the photos posted in there, you can see they’re more than three pair of legs.
  2. Britannica page on insects: Insects are distinguished from other arthropods by their body…which usually has three pairs of legs

Disease/microbes (2)

Q1. Which method of water purification does not kill microorganism?

  1. Boiling
  2. Filtration
  3. Chlorination
  4. UV-irradiation

Although common sense suggest answer should be filtration among the given option. But for the sake of reference: FAQ page of a UV filter company

Do ordinary filters kill bacteria?

No. Ordinary filters cannot kill bacteria. The bacteria will enter the filter and either pass through the filter or grow within the filter.

Hence answer (B).

Q2. What causes dough (a mixture of flour, water, etc.) to rise when yeast is added to it?

  1. An increase in the temperature
  2. An increase in the amount of the substance
  3. An increase in the number of yeast cells
  4. Release of carbon dioxide gas

NCERT 7 Ch. 10 page 1

there are some organisms such as yeast that can survive in the absence of air.  They are called anaerobes. They get energy through anaerobic respiration. In the absence of oxygen, they breakdown glucose into alcohol and carbon dioxide. => Answer should be D.

Britannica confirms

leavening agent cause expansion of doughs by the release of gases within such mixtures, thus, producing baked products with porous structure. Yeast, baking powder, and baking soda are examples of leavening agents.

Final answer (D)

Human Biology(6)

Q1. Deficiency of which of the following elements is responsible for weakening of bones?

  1. Calcium
  2. Phosphorus
  3. Nitrogen
  4. Carbon

Select the correct answer using the code given below.

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

Common sense suggests answer should be only 1 (Calcium). but this is UPSC, so before applying common sense we should cross check that atleast #2 (phosphorous) is wrong. (if phosphorous is wrong, then it’ll automatically eliminate “A” and “C”)

NCERT Class 12 Chemistry Ch 7 Page 2.

Phosphorus is an essential constituent of animal and plant matter. It is present in bones as well as in living cells.

But, will its deficiency weaken the bone?

  1. Britannica Kids: A diet deficient in vitamin D, calcium, or phosphorus, can result in rickets.. causes bone deformities such as bowlegs.
  2. Encyclopedia of Animal Science by Wilson G. Pond Page 636: The outstanding disease of Ca and P deficiency is rickets. Rickets results in weak bones, causing curving and bending of the bones.
  3. Food and nutrition education, Punam Chopra, Page 123: In Children, phosphorous deficiency causes weakening of teeth and bones.

Therefore, answer (A) only 1 and 2. i.e. deficiency of calcium and phosphorous leads to weakening of bones.

Q2. Which of the following statements is/are correct regarding fats?

  1. Fats are needed for the formation of cell membrane.
  2. Fats help the body to absorb calcium from food.
  3. Fats are required to repair damaged tissue.
  4. Body cannot release energy in fats as quickly as the energy in carbohydrates.

Select the correct answer using the code given below.

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

Statement #1 is correct

  1. theHindu from 2010: Fifty per cent of all our cell membranes are made up of saturated fat.
  2. Cellular physiology, Livio Luzi, Page18: The three main classes of lipids that makeup the cell membranes are fats, phospholipids and steroids

Statement 4 is correct

  1. Energy Balance by Westerterp, Page 34: Carbohydrate is a fast energy source. Fat as an energy source only becomes available through a longer digestion process.
  2. Advanced Marathoning By Pete Pfitzinger, Page 37: Carbohydrate is a more efficient energy source than fat. You cannot run as fast by burning just fat.

Final answer: (A) 1 and 4

Q3. Which of-the following statements is /are correct?

  1. Amnion contains fluid.
  2. Ultrasound scan can detect the sex of an embryo.

Select the correct answer using the code given below.

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

Statement #1 is right, as per Britannica

Amnion is a membrane forming a fluid-filled cavity (the amniotic sac) that encloses the embryo in reptiles, birds, and mammals

Statement #2 is right. Although we all know it but for the sake of reference: Textbook of Basic nursing, Nursine by aroline Rosdahl and Mary Kowalski, Page 949

Ultrasound scan can determine the age, size and sex of the foetus.

counter argument: Ultrasound cannot detect @”Embryo” stage.

Answer (C) or A.

Q4.Two strands of DNA are held together by

  1. hydrogen bonds
  2. covalent bonds
  3. electrostatic force
  4. van der Waals’ forces

Page 519 of Lucent GK Book =>answer A

Q5.Match List-I with List-II and select the answer using the code given below the Lists:

List-I(Gland) List-II(Hormone)
A.Pancreas 1.Cortisol
B.Pituitary 2.Vitamin D
C.Adrenals 3.Thyroid stimulating hormone
D.Kidneys 4.Glucagon


a 4 3 1 2
b 4 1 3 2
c 2 1 3 4
d 2 3 1 4

correct pairs

A4: Pancreas (alpha cells) =Glucagon NCERT 11 Biology, ch 22 page 7
B3: Pituitary = Thyroid page3
C1: Adrenal = Cortisol page 6

There is only one option A where such pattern emergences. Hence answer (A)

Source#2: Lucent GK Book Page 554-555

Source#3: TMH General Studies Manual, Page 110

Q6. People suffering from anorexia nervosa

  1. Develop paralysis
  2. Show poor reflex
  3. Cannot speak properly
  4. Eat very little and fear gaining weight

NCERT 12 Psychology Ch.4 Page 16

In anorexia nervosa, the individual has a distorted body image that leads her/him to see herself/himself as overweight.  Often refusing to eat, exercising compulsively and developing unusual habits such as refusing to eat in front of others, the anorexic may lose large amounts of weight and even starve herself/himself to death. Hence answer (D).

Another source: in the same book, Glossary, page 1.

— THE END of Science answerkey —

Any correction/update- mention in the comments. But avoid Wikipedia as reference source.
Remaining subjects (geography, Environment-biodiversity, economy, current etc.) coming soon. Visit Mrunal.org/CDS for more on Combined defense services exam and SSB interviews.