UPSC CDS-2

41. Which among the following methods is used to separate the constituents

Which among the following methods is used to separate the constituents present in a compound ?

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Electrochemical method
Heating method
Fractional distillation
Decomposition followed by ion exchange
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To separate the constituents (elements) present in a compound, chemical bonds must be broken. This process is called decomposition. Decomposition requires energy and can be achieved through various methods, including using electricity (electrolysis), heat (thermal decomposition), or light (photolysis). Electrochemical methods, such as electrolysis, are used to decompose certain compounds (like water or molten salts) into their constituent elements by passing an electric current through them.
Separating constituents of a compound involves breaking chemical bonds, which is a chemical process (decomposition). This is distinct from separating components of a mixture, which involves physical methods like distillation, filtration, etc.
Option B, Heating method (thermal decomposition), is also a valid method to decompose some compounds, but not all. Option C, Fractional distillation, is a technique used to separate liquids with different boiling points from a *mixture*, not to separate elements bonded within a compound. Option D, Decomposition followed by ion exchange, is a specific process for separating ions after decomposition, but the decomposition itself is the key step in breaking down the compound. Among the given options, Electrochemical method represents a fundamental way to chemically decompose compounds into their constituents.

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42. How much percentage of carbon dioxide is present in the atmosphere of

How much percentage of carbon dioxide is present in the atmosphere of Venus and Mars ?

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45 - 47%
52 - 55%
74 - 77%
95 - 97%
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The atmospheres of both Venus and Mars are predominantly composed of carbon dioxide. Venus’s atmosphere is about 96.5% CO2, and Mars’s atmosphere is about 95% CO2. Option D, 95 – 97%, is the range that accurately represents the high percentage of carbon dioxide in the atmospheres of both planets.
The thick CO2 atmosphere of Venus creates an extreme greenhouse effect, resulting in very high surface temperatures. The thin CO2 atmosphere of Mars contributes to its cold and arid conditions.
In contrast, Earth’s atmosphere is composed primarily of nitrogen (about 78%) and oxygen (about 21%), with carbon dioxide being only a trace gas (around 0.04%), although its concentration is increasing due to human activities. The composition of planetary atmospheres is a key factor determining their climate and potential for life.

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43. Which one among the following are the correct symbols for the elements

Which one among the following are the correct symbols for the elements gold, tin and lead, respectively ?

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Ga, Sb, Pb
At, Sn, Le
Au, Sn, Pb
Au, Sb, Pb
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The question asks for the correct chemical symbols for the elements gold, tin, and lead, respectively. The internationally recognized symbols are Au for gold, Sn for tin (from its Latin name Stannum), and Pb for lead (from its Latin name Plumbum).
Chemical symbols are standard abbreviations used to represent elements. Many symbols are derived from the element’s English name (e.g., O for Oxygen, H for Hydrogen), but some are derived from their historical Latin or Greek names to maintain uniqueness and historical consistency.
Option A lists Ga (Gallium), Sb (Antimony), Pb (Lead). Option B lists At (Astatine), Sn (Tin), Le (not a standard symbol). Option D lists Au (Gold), Sb (Antimony), Pb (Lead). Only option C provides the correct symbols for all three elements: Au, Sn, and Pb.

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44. Sonic boom is produced when a source of sound travels at a speed :

Sonic boom is produced when a source of sound travels at a speed :

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greater than the speed of sound.
greater than the speed of light.
lesser than the speed of sound.
equal to the speed of sound.
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The correct answer is A) greater than the speed of sound.
A sonic boom is a loud sound produced when an object, such as an aircraft, travels through the air faster than the speed of sound. When an object moves at supersonic speed (Mach number greater than 1), it creates shock waves as it compresses the air ahead of it. These shock waves propagate outwards and reach the listener’s ears as a ‘boom’.
The speed of sound varies depending on the medium and its temperature and pressure. At sea level in standard atmospheric conditions (15°C), the speed of sound in air is approximately 343 meters per second (or 1,236 kilometers per hour, or 767 miles per hour). Objects travelling at speeds less than the speed of sound are called subsonic, at the speed of sound are transonic or sonic (Mach 1), and greater than the speed of sound are supersonic or hypersonic (Mach > 5).

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45. If the Moon is brought closer to the Earth such that its distance from

If the Moon is brought closer to the Earth such that its distance from the Earth becomes half of the original distance, then the gravitational force of attraction between the Earth and the Moon would :

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reduce to half of its original value.
increase to two times of its original value.
remain the same as the original value.
increase to four times of its original value.
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The correct answer is D) increase to four times of its original value.
According to Newton’s Law of Universal Gravitation, the gravitational force (F) between two objects with masses M₁ and M₂ is directly proportional to the product of their masses and inversely proportional to the square of the distance (r) between their centers: F = G * (M₁ * M₂) / r².
In this case, M₁ is the mass of the Earth (M_earth) and M₂ is the mass of the Moon (M_moon). Let the original distance be r. The original gravitational force is F = G * (M_earth * M_moon) / r².
If the distance is halved, the new distance is r’ = r/2. The new gravitational force F’ will be:
F’ = G * (M_earth * M_moon) / (r’)²
F’ = G * (M_earth * M_moon) / (r/2)²
F’ = G * (M_earth * M_moon) / (r²/4)
F’ = 4 * [G * (M_earth * M_moon) / r²]
So, F’ = 4 * F. The gravitational force increases to four times its original value.
This inverse square relationship means that if the distance is reduced by a factor, the force increases by the square of that factor. Conversely, if the distance were doubled, the force would reduce to (1/2)², or one-fourth, of its original value. This law governs gravitational interactions throughout the universe.

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46. A concave mirror of radius of curvature 50 cm is used to form an image

A concave mirror of radius of curvature 50 cm is used to form an image of an object kept at a distance of 25 cm from the mirror on its principal axis. What will be the position of the image from the mirror ?

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At infinity
At 50 cm
At 25 cm
At 75 cm
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The correct answer is A) At infinity.
The radius of curvature (R) of a concave mirror is 50 cm. The focal length (f) of a spherical mirror is half the radius of curvature, so f = R/2 = 50 cm / 2 = 25 cm. For a concave mirror, the focal length is considered negative in standard sign conventions when light comes from the left, so f = -25 cm. The object is kept at a distance of 25 cm from the mirror, which means the object distance (u) is -25 cm (object is real, placed on the left).
We use the mirror formula: 1/f = 1/v + 1/u, where v is the image distance.
Substituting the values: 1/(-25) = 1/v + 1/(-25)
-1/25 = 1/v – 1/25
1/v = -1/25 + 1/25
1/v = 0
This implies v = infinity.
When an object is placed at the focal point of a concave mirror, the rays of light from the object become parallel after reflection. Parallel rays meet at infinity, hence forming a real, inverted, and infinitely large image at infinity. This principle is used in devices like searchlights and headlights, where a light source is placed at the focus to produce a parallel beam of light.

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47. Consider a journey by a car represented by the graph given below in th

Consider a journey by a car represented by the graph given below in three parts A, B and C. The speed of the car in these parts is va, vb and vc, respectively :
[Image shows a Distance vs Time graph with segments O-A, A-B, B-C representing the journey parts]
Which one of the following is correct in this case ?

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”v<sub>a</sub>
”v<sub>b</sub>
”v<sub>a</sub>
”v<sub>a</sub>
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The correct answer is D) va > vb; va > vc.
In a distance vs. time graph, the speed is represented by the slope of the graph (speed = change in distance / change in time).
– Part A (O-A): The graph is a straight line with a positive slope, indicating constant positive speed. The slope is relatively steep.
– Part B (A-B): The graph is a horizontal line, meaning the distance is not changing over time. The slope is zero, indicating the car is stopped (vb = 0).
– Part C (B-C): The graph is a straight line with a positive slope, indicating constant positive speed. The slope is less steep than in Part A.
Comparing the slopes: Slope of A > Slope of C > Slope of B (which is 0). Therefore, va > vc > vb.
Looking at the options, D) va > vb; va > vc is the only option that correctly reflects the relationship va > vc and va > vb (since vb = 0).
A steeper slope on a distance-time graph indicates a higher speed, while a less steep slope indicates a lower speed. A horizontal line means the object is at rest, and a line with a negative slope would indicate movement back towards the starting point.

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48. A person can see near objects clearly through his eyes but cannot see

A person can see near objects clearly through his eyes but cannot see distant objects clearly. The possible reason(s) for this defect could be :

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  • 1. Excessive curvature of the eye lens.
  • 2. The eye-ball has become too small.
  • 3. The focal length of the eye lens is too large.
  • 4. Elongation of the eye-ball.

Select the correct answer using the code given below :

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1 only
2 and 4 only
1 and 4 only
1 and 3 only
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The correct answer is C) 1 and 4 only.
The condition described, seeing near objects clearly but not distant objects clearly, is known as Myopia or short-sightedness. Myopia occurs when the image of distant objects is focused in front of the retina instead of directly on it. This can be caused by:
1. Excessive curvature of the eye lens: This increases the refractive power of the lens, causing light rays to converge too strongly.
2. Elongation of the eye-ball: If the eyeball is too long from front to back, the retina is located behind the point where the image is focused by a lens of normal power.
Options 2 (eye-ball too small) and 3 (focal length of the eye lens is too large – which implies weaker power) would typically lead to Hypermetropia (far-sightedness), where the image is focused behind the retina.
Myopia is corrected by using a concave lens (diverging lens) which diverges the light rays before they enter the eye, causing them to focus further back, onto the retina. Hypermetropia is corrected using a convex lens (converging lens). Presbyopia, another common vision defect, is the loss of the eye’s ability to focus actively on nearby objects due to the hardening of the lens, usually occurring with age.

49. Which one among the following reports defines Sustainable Development

Which one among the following reports defines Sustainable Development as development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs ?

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Brundtland Report
United Nations Human Development Report
Agenda-21 of the Rio Earth Summit
OECD Policy Brief (2006)
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The correct answer is A) Brundtland Report.
The definition of sustainable development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” was famously articulated in “Our Common Future,” the 1987 report of the World Commission on Environment and Development (WCED), chaired by Gro Harlem Brundtland. This report is widely referred to as the Brundtland Report.
This definition became the standard for sustainable development globally. Agenda 21 was the comprehensive action plan for sustainable development adopted at the 1992 United Nations Conference on Environment and Development (UNCED), also known as the Earth Summit, held in Rio de Janeiro. It built upon the principles laid out in the Brundtland Report but did not originate the definition. The UN Human Development Report series focuses on measuring human development, and OECD reports discuss various policy areas, including sustainable development, but none of these originated the iconic definition from 1987.

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50. The ‘Ramsar Convention’ relates to which one of the following areas ?

The ‘Ramsar Convention’ relates to which one of the following areas ?

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Wetland preservation
Promote afforestation
Action plan on climate change
Combat desertification
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The correct answer is A) Wetland preservation.
The Ramsar Convention, officially known as the Convention on Wetlands of International Importance especially as Waterfowl Habitat, is an international treaty signed in Ramsar, Iran, in 1971. Its primary focus is the conservation and sustainable use of wetlands and their resources.
Wetlands are defined by the convention as areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres. The convention provides a framework for international cooperation for the conservation of wetland habitats.

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