UPSC NDA-2 Archives

41. Which one from among the following planets is largest in size ?

Which one from among the following planets is largest in size ?

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Earth

Venus

Mars

Mercury

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Earth is the largest planet in size among the given options.

Comparing the approximate mean diameters of the planets listed:
– Mercury: ~4,880 km
– Venus: ~12,100 km
– Earth: ~12,740 km
– Mars: ~6,780 km

Among Mercury, Venus, Earth, and Mars, Earth has the largest diameter and is therefore the largest in size. The order from largest to smallest among these is Earth > Venus > Mars > Mercury. In the entire solar system, the planets in order of decreasing size are Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, and Mercury.

42. In case of a concave mirror, if an object is kept between principal fo

In case of a concave mirror, if an object is kept between principal focus F and pole P of the mirror, then which one of the following statements about the image is NOT correct ?

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The image will be virtual

The image will be enlarged or magnified

The image will be formed at infinity

The image will be erect

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The statement “The image will be formed at infinity” is NOT correct.

When an object is placed between the principal focus (F) and the pole (P) of a concave mirror, the reflected rays diverge but appear to originate from a point behind the mirror. This forms a virtual image.

For a concave mirror with an object between F and P:
– The image is formed behind the mirror.
– The image is virtual (cannot be projected on a screen).
– The image is erect (upright relative to the object).
– The image is magnified (larger than the object).
An image is formed at infinity by a concave mirror only when the object is placed exactly at the principal focus (F). When the object is between F and P, the image is virtual and located at a finite distance behind the mirror.

43. The refractive index of fused quartz is 1.46 and that of sapphire is 1

The refractive index of fused quartz is 1.46 and that of sapphire is 1.77. If v_q is the speed of light in quartz and v_s is the speed of light in sapphire, then which one of the following relations is correct ?

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”v<sub>q</sub>

”v<sub>s</sub>

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The relation v_q > v_s is correct.

The refractive index (n) of a medium is inversely proportional to the speed of light (v) in that medium, according to the formula n = c/v, where c is the speed of light in a vacuum. Therefore, v = c/n. A higher refractive index means a lower speed of light, and a lower refractive index means a higher speed of light.

Given n_q = 1.46 and n_s = 1.77. Since n_s > n_q, it follows that v_s = c/n_s must be less than v_q = c/n_q. Hence, v_q > v_s. The speed of light is slower in sapphire than in fused quartz because sapphire has a higher refractive index.

44. Which one of the following was the first mineral acid discovered ?

Which one of the following was the first mineral acid discovered ?

Sulphuric acid

Hydrochloric acid

Nitric acid

Phosphoric acid

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Nitric acid was one of the first mineral acids discovered.

Mineral acids are acids derived from inorganic compounds. Historically, strong mineral acids like nitric acid, sulfuric acid, and hydrochloric acid were developed by alchemists and early chemists during the Middle Ages. Nitric acid (aqua fortis) is often credited to the Arab alchemist Jabir ibn Hayyan (Geber) in the 8th century, produced by distilling saltpetre (potassium nitrate) with vitriol (sulfates).

While the precise historical order and attribution can be complex due to the nature of early chemical writings, nitric acid is widely recognized as one of the earliest strong mineral acids whose preparation from mineral sources was documented. Sulphuric acid and hydrochloric acid were also known and developed around similar periods by various alchemists like Al-Razi. Phosphoric acid was discovered later, notably by Hennig Brand in the 17th century.

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45. Which one of the following is the best example of desiccant ?

Which one of the following is the best example of desiccant ?

Silica gel

Polystyrene

Sodium chloride

Sodium carbonate

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Silica gel is the best example of a desiccant among the given options.

A desiccant is a substance that absorbs or adsorbs water, thus creating or maintaining a state of dryness. Silica gel is widely used for this purpose due to its porous structure, which allows it to adsorb a significant amount of water vapour.

Silica gel is often found in small packets in product packaging (like electronics, shoes, leather goods, etc.) to protect them from moisture damage. While other substances like calcium chloride or activated alumina are also used as desiccants, silica gel is a common and effective example. Polystyrene is a type of plastic. Sodium chloride (common salt) can absorb moisture (hygroscopic) but is not primarily used as a general industrial desiccant in the same way as silica gel. Sodium carbonate can absorb moisture to form hydrates but is also not the primary example of a desiccant.

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46. Which one of the following statements regarding Bleaching powder and D

Which one of the following statements regarding Bleaching powder and D.D.T. is correct ?

Both are inorganic compounds

Both are organic compounds

Both contain chlorine

Both contain calcium

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The correct answer is (C) Both contain chlorine.

Let’s look at the chemical composition of both substances:
– Bleaching powder is Calcium oxychloride (CaOCl2). It is an inorganic compound containing calcium and chlorine.
– D.D.T. is Dichloro-diphenyl-trichloroethane ((ClC6H4)2CH(CCl3)). It is an organic compound (containing carbon and hydrogen, with chlorine substituents) containing chlorine but no calcium.
Comparing the options:
A) Both are inorganic compounds: False (DDT is organic).
B) Both are organic compounds: False (Bleaching powder is inorganic).
C) Both contain chlorine: True (Bleaching powder has chlorine, and DDT has multiple chlorine atoms).
D) Both contain calcium: False (DDT does not contain calcium).

Bleaching powder is used as a bleaching agent and disinfectant. DDT was a widely used insecticide but is now banned or restricted in many countries due to its environmental persistence and harmful effects.

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47. Which one of the following is the correct sequence of change in colour

Which one of the following is the correct sequence of change in colours when a turmeric stain on white clothes is scrubbed by soap and then washed with water ?

Yellow – pink – blue

Yellow – reddish brown – yellow

Yellow – reddish brown – blue

Yellow – blue – pink

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The correct answer is (B) Yellow – reddish brown – yellow.

Turmeric is a natural acid-base indicator. Its original colour is yellow. In acidic or neutral solutions, it remains yellow. In basic (alkaline) solutions, it turns reddish-brown. Soap solution is basic. Therefore, when a turmeric stain (yellow) on white clothes is scrubbed with soap, it turns reddish-brown. When the cloth is then washed with plain water, which is usually neutral or slightly acidic due to dissolved CO2, the basic soap is rinsed away, and the turmeric indicator returns to its yellow colour.

Other indicators change colours differently in acidic and basic media. For example, litmus paper is red in acid and blue in base; phenolphthalein is colourless in acid and pink in base. Turmeric’s characteristic change from yellow to reddish-brown is a common demonstration of its indicator property.

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48. Number of molecules of water of crystallization in copper sulphate, so

Number of molecules of water of crystallization in copper sulphate, sodium carbonate and Gypsum are

5, 10 and 2 respectively

10, 2 and 5 respectively

5, 2 and 10 respectively

2, 5 and 10 respectively

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The correct answer is (A) 5, 10 and 2 respectively.

The number of molecules of water of crystallization are specific to the hydrated forms of these compounds:
– Copper sulphate exists commonly as copper(II) sulphate pentahydrate, CuSO4·5H2O, which has 5 molecules of water.
– Sodium carbonate exists commonly as sodium carbonate decahydrate (washing soda), Na2CO3·10H2O, which has 10 molecules of water.
– Gypsum is calcium sulphate dihydrate, CaSO4·2H2O, which has 2 molecules of water.

Water of crystallization refers to water molecules that are chemically bonded to ions in the crystal structure of a salt. These water molecules are part of the crystalline structure but can be removed by heating the salt.

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49. At nearly 70°C, sodium bicarbonate shows the property of gradually dec

At nearly 70°C, sodium bicarbonate shows the property of gradually decomposing, which makes it usable in bakery products. The product of decomposition responsible for this use of sodium bicarbonate is

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Carbon dioxide

Hydrogen

Water vapour

Oxygen

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The correct answer is (A) Carbon dioxide.

Sodium bicarbonate (baking soda, NaHCO3) is used in bakery products as a leavening agent. When heated, it decomposes according to the reaction: 2NaHCO3(s) → Na2CO3(s) + H2O(g) + CO2(g). The gaseous products, water vapour and especially carbon dioxide, are trapped within the dough, causing it to expand and become light and porous. Carbon dioxide is the primary gas responsible for the leavening action.

The resulting sodium carbonate (Na2CO3) is a residual solid. While water vapour also contributes to the rise, carbon dioxide is the main leavening gas produced from this decomposition at baking temperatures. Hydrogen and oxygen are not significant products of this specific decomposition reaction.

50. A lens has a power of +2.0 Dioptre. Which one of the following stateme

A lens has a power of +2.0 Dioptre. Which one of the following statements about the lens is true ?

The lens is concave and has a focal length of 0.5 metre

The lens is convex and has a focal length of 2.0 metre

The lens is convex and has a focal length of 0.5 metre

The lens is concave and has a focal length of 2.0 metre

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The correct answer is (C) The lens is convex and has a focal length of 0.5 metre.

The power of a lens (P) is the reciprocal of its focal length (f) when the focal length is measured in meters. The formula is P = 1/f. Given the power P = +2.0 Dioptre, the focal length f = 1/P = 1/2.0 = 0.5 meters. A positive power indicates a converging lens, which is a convex lens.

Concave lenses have negative power and diverge light. Convex lenses have positive power and converge light (for real objects). The unit of power is Dioptre (D), where 1 D = 1 m⁻¹.

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