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UPSC

Explore popular questions from Everyday Science for UPSC. This collection covers Everyday Science previous year UPSC questions hand picked by experienced teachers.

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Q 1. An iron needle sinks in water whereas a ship made of iron floats on it because

A

the edge of the needle is pointed

B

the ship is flat

C

the ship is driven by powerful engine

specific gravity of the needle is greater than that of water displaced by it.

Explanation

Because the specific gravity of the needle is greater than that of water displaced by it.
{tex}\text {Specific gravity (or relative density)}=\frac{\text {Density of the substance}}{\mathrm {Density \ of \ water \ at \ 4^{\circ} C}}{/tex}
The average density of iron needle is greater than water, therefore, it sinks.

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Q 2. An astronaut orbiting the earth in a circular orbit 120 km above the surface of earth, gently drops a spoon out of the space ship. The spoon will

A

fall vertically down to the earth

B

move towards the moon

will move along with the space ship

D

will move in an irregular way and then fall down to earth

Explanation

When spoon is dropped gently, its tangential speed is equal to the speed of spaceship, and so it revolves like a satellite.

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Q 3. Alum purifies muddy water by

A

Absorption

B

Dialysis

C

Emulsification

Coagulation

Explanation

Coagulation is the process of accumulation and setting down of particles present in a colloidal solution. Aluminium Sulphate, also known as Alum, when added to water reacts with the bicarbonate alkalinities present in water and forms a gelatinous precipitate. This floc attracts other fine particles and suspended material in water, and settles down at the bottom of the container.

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Q 4. Which of the statements given below is/are correct? Permanent hardness of water is due to the presence of soluble.
1. chloride of calcium
2. bicarbonate of calcium
3. sulphate of magnesium
4. bicarbonate of magnesium
Select the correct answer using the codes given below.

A

1 only

1 and 3

C

2 and 4

D

1,2 and 3

Explanation

Chlorides and sulphates of calcium and magnesium are responsible for permanent hardness of water.
Note: Bicarbonates are responsible for temporary hardness of water.

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Q 5. Why ethylene dibromide is added to petrol -
1. It increases the octane number of fuel
2. It helps in elimination of lead oxide
3. It removes the sulphur compound in petrol
4. It serves as a substitute of tetraethyl lead

A

1 and 2

B

2 and 3

C

1 only

2 only

Explanation

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

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Q 6. Consider the following statements :
(i) Washing soda on strong heating gives sodium oxide and carbon dioxide.
(ii) Plaster of Paris is obtained by heating gypsum at 373 K.
(iii) Bleaching powder is used for disinfecting drinking water.
Which of these statement(s) is/are correct ?

A

(i) and (ii)

(ii) and (iii)

C

(i) and (iii)

D

All are correct

Explanation

Washing soda is sodium salt of carbonic acid. It occurs as a crystalline heptahydrate, which on heating looses its water to form a white powder monohydrate. This process is called efflorescence.
{tex}\mathrm {NaCO_3.7H_2O \xrightarrow{heat} Na_2CO_3.H_2O + 6H_2O}{/tex}

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Q 7. Given:
1. Blood cells 2. Bone cells
3. Hair strands 4. Saliva Samples taken for DNA testing in criminal investigation can be

A

1,2 and 3 only

B

land 4 only

C

2 and 3 only

1,2, 3 and 4 only

Explanation

For DNA testing biological samples are required, this include all biological fluids, tissues which contain the undegraded genetic material.

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Q 8. In which of the following conditions wet clothes will dry earliest?

A

100% RH, 60°C temperature

B

100% RH, 20°C temperature

C

20% RH, 20°C temperature

20% RH, 60°C temperature

Explanation

Wet clothes will dry earlier when the humidity of the environment will be lowest and temperature will be the maximum.

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Q 9. While lifting a bucket of water from a well, we feel that the bucket

becomes heavier above the surface of water.

B

becomes lighter above the surface of water.

C

looses stability on coming out of water.

D

has gained mass on coming out of water.

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Q 10. The leaning tower of Pisa does not fall because

A

it is tappered at the top

B

it covers a large base area

C

its centre of gravity remains at the lowest position

the vertical line through the centre of gravity of the tower falls within the base

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Q 11. The‘blue moon’phenomenon occurs

when two full moons occur in the same month.

B

when four full moons appear in two consecutive months of the same calendar year.

C

when two full moons appear in the same month thrice in a calendar year

D

none of the above

Explanation

The blue Moon phenomenon occurs when two full moon occur in the same month. Such an incident had taken place in 1999 when two full moons had taken place in the January and February of the same years.

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Q 12. In an earthen pitcher, the water remains cold due to the process of

A

Condensation

Evaporation

C

Sublimation

D

None of the above

Explanation

Continuous evaporation through minute pores on the surface of earthen pitcher causes evaporation and thus water inside it remains cool.

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Q 13. White colour of milk is due to the presence of

A

lactose

B

albumins

C

carotenes

caseins

Explanation

Many factors influence colour of milk including presence of milk protein casein.

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Q 14. Which one of the following gases is used for the purification of drinking water?

A

Sulphur dioxide

Chlorine

C

Fluorine

D

Carbon dioxide

Explanation

Chlorination is the process of using chlorine for treatment of water making it suitable for drinking purposes. Amount of chlorine gas required for water treatment may vary depending upon water quality.

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Q 15. Pheromones are generally produced by

A

Snakes

B

Birds

C

Bats

Insects

Explanation

Pheromones are substances which are secreted to the outside by an individual and received by a second individual of the same species. Although it is secreted by a range of organisms, its effect is more prominent in insects.

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Q 16. Earthquake (shock) waves are

A

infrasonic waves

B

ultrasonic waves

seismic

D

infrared waves

Explanation

An Earthquake is the result of a sudden release of energy in the Earth’s crust that creates seismic waves.

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Q 17. Fat can be separated from milk in a cream separation because of

A

cohesive force

B

gravitational force

centrifugal force

D

centripetal force

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Q 18. Raw mangoes shrivel when pickled in brine. The phenomenon is associated with

osmosis

B

reverse osmosis

C

increase of surface tension of fluid

D

decrease of surface tension of fluid

Explanation

Raw mangoes shrivel when pickled in brine due to osmosis i.e. flow of water from higher concentration to lower concentration through a semi-permeable membrane.

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Q 19. Half portion of a rectangular piece of ice is wrapped with a white piece of cloth while the other half with a black one. In this context, which one among the following statements is correct?

Ice melts more easily under black wrap

B

Ice melts more easily under white wrap

C

No ice melts at all under the black wrap

D

No ice melts at all under the white wrap

Explanation

Ice under black wrap will melt easily because dark colour (black) absorbs the most of light energy falling on it.

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Q 20. If a ship moves from freshwater into seawater, it will

A

sink completely

B

sink a little bit

rise a little higher

D

remain unaffected

Explanation

When a body is immersed in a fluid, the fluid exerts an upward force on it, called buoyant force.
and buoyant force {tex}\propto{/tex} density of fluid.
As the density of sea water is higher than that of the fresh water.
So extra buoyant force and ship will rise a little higher.

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Q 21. The cat can survive fall from a height much more than human or any other animal. It is because the cat

can immediately adjust itself to land on all four paws and bend the legs to absorb the impact of falling

B

has clastic bones

C

has thick and elastic skin

D

also gets injury equally with other animals, but has tremendous endurance, resistance and speedy recovery

Explanation

As the cat falls from a height, it bends the legs to absorb the impact of falling and immediately adjust itself.

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Q 22. Fire fly gives us cold light by virtue of the phenomenon of

A

fluorescence

B

phosphorescence

chemiluminescence

D

effervescence

Explanation

Fire fly gives us cold light due to chemiluminescence i.e. light produced by chemical reaction.

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Q 23. The best colours for a sun umbrella will be

A

black on top and red on inside

B

black on top and white on inside

C

red on top and black on inside

white on top and black on inside

Explanation

As white colour reflects all the components of white light and black colour absorbs all the components of white light. So, the best colours for a sun umbrella, white on top and black on inside.

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Q 24. When ice melts, its

volume decreases

B

volume increases

C

volume and mass both decrease

D

volume decreases while mass increases

Explanation

When ice melts its density increases i.e. its volume decreases. Mass is a invariant quantity.

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Q 25. When deep sea fishes are brought to the surface of the sea, their bodies burst. This is because the blood in their bodies flows at very

high speed

B

high pressure

C

low speed

D

low pressure