UPSC NDA-2 Archives

21. Which one of the following statements is not correct?

Which one of the following statements is not correct?

In steady flow of a liquid, the velocity of liquid particles reaching at a particular point is the same at all points

Steady flow is also called streamlined flow

In steady flow, each particle may not follow the same path as taken by a previous particle passing through that point

Two streamlines cannot intersect each other

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UPSC NDA-2 – 2015

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The correct answer is C) In steady flow, each particle may not follow the same path as taken by a previous particle passing through that point. This statement is incorrect. In steady flow (or streamlined flow), the velocity of the fluid at any given point in space is constant over time. Consequently, the path followed by every fluid particle passing through a particular point is the same as the path followed by previous particles passing through that same point. These paths are called streamlines.

In steady flow, streamlines are fixed paths in space, and fluid particles follow these fixed paths.

Statement A is poorly phrased but likely intends to convey that velocity at a fixed point is constant over time, which is true for steady flow, though the “at all points” part is confusing. Statement B is correct; steady flow is also known as streamlined flow. Statement D is correct; streamlines cannot intersect because if they did, a fluid particle at the intersection would have two different velocity vectors simultaneously, which is physically impossible.

22. Which one of the following is useful in the paper manufacturing

Which one of the following is useful in the paper manufacturing industry?

Fibrous plants

Orchids

Non-flowering plants

Plants growing in high altitude

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UPSC NDA-2 – 2015

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The correct answer is A) Fibrous plants. Paper is primarily made from cellulose fibers, which are obtained from plants. Fibrous plants, particularly trees (wood pulp) and other plants like bamboo, cotton, and hemp, are rich in these fibers and are the main raw materials for the paper manufacturing industry.

Paper production relies on extracting cellulose fibers from plant sources.

While other plants exist (like orchids, non-flowering plants, high-altitude plants), the key characteristic relevant to paper making is the presence of suitable fibers. Orchids are not used for paper. Non-flowering plants is too broad; while some non-flowering plants like conifers are used, the term “fibrous plants” is a more direct description of the useful property. Plants growing in high altitude is irrelevant to their suitability for paper making based on fiber content.

23. The alkali metals have relatively low melting point. Which one of the

The alkali metals have relatively low melting point. Which one of the following alkali metals is expected to have the highest melting point?

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UPSC NDA-2 – 2015

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The alkali metals are in Group 1 of the periodic table: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs), and Francium (Fr). Moving down the group, the metallic bonding strength generally decreases due to the increasing atomic size and shielding effect, which weakens the attraction between the positive ions and the delocalized valence electrons. Weaker metallic bonding leads to lower melting points. Therefore, the melting points of alkali metals decrease down the group. Among the options provided (Li, Na, K, Rb), Lithium is at the top of the group and is expected to have the highest melting point.

Melting points of alkali metals decrease down the group (from Li to Fr) due to decreasing metallic bond strength.

The approximate melting points are: Li (180.5 °C), Na (97.8 °C), K (63.5 °C), Rb (39.3 °C), Cs (28.5 °C). As expected, Lithium has the highest melting point among the given options. This trend is a typical example of how physical properties change across a group in the periodic table.

24. Which one of the following statements is not correct?

Which one of the following statements is not correct?

Application of lime makes the soil acidic.

High acidity in soil is typical of humid climate.

Increasing soil acidity results in declining soil fertility.

Arid climate is characterized by alkaline soil.

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UPSC NDA-2 – 2015

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Let’s analyze each statement about soil acidity:
A) Application of lime (usually calcium carbonate, CaCO₃, or calcium oxide, CaO, which reacts with water to form calcium hydroxide, Ca(OH)₂) is a common agricultural practice used to *reduce* soil acidity and increase pH, making the soil more alkaline or neutral. Therefore, applying lime does not make the soil acidic; it makes it less acidic. This statement is not correct.

Lime is applied to soil to neutralize acidity (increase pH), not to make it acidic.

B) High acidity in soil is typical of humid climates where high rainfall leads to leaching of basic cations (Ca²⁺, Mg²⁺, K⁺, Na⁺) from the topsoil, leaving behind acidic ions like H⁺ and Al³⁺.
C) Increasing soil acidity can lead to declining soil fertility because essential plant nutrients (like phosphorus) become less available, and potentially toxic elements (like aluminum and manganese) become more soluble and available at low pH levels.
D) Arid climates are characterized by low rainfall, which limits the leaching of basic cations. Evaporation can also bring dissolved salts to the surface, often resulting in the accumulation of carbonates and other salts that contribute to alkalinity. Hence, arid soils are often alkaline or saline.
Since the question asks for the statement that is *not* correct, option A is the answer.

25. Which one of the following statements is correct?

Which one of the following statements is correct?

Rutherford’s alpha-particle scattering experiment led to the discovery of electron.

J J Thomson suggested that the nucleus of an atom contains protons.

The atomic number of an element is the same as the number of protons in the nucleus of its atom.

The mass number of an atom is equal to the number of electrons in its shells.

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UPSC NDA-2 – 2015

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Let’s analyze each statement:
A) Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic *nucleus*, not the electron. The electron was discovered by J.J. Thomson through his cathode ray experiments.
B) J J Thomson proposed the ‘plum pudding’ model, where electrons were embedded in a diffuse positive charge. Rutherford, based on his experiment, proposed the nuclear model with a central positive nucleus containing protons and neutrons (neutrons were discovered later by Chadwick).
C) The atomic number (Z) of an element is defined as the number of protons in the nucleus of an atom of that element. This statement is correct.
D) The mass number (A) of an atom is the total number of protons and neutrons in the nucleus (A = Z + N). It is not equal to the number of electrons in its shells (unless the atom is neutral, but even then, mass number is protons + neutrons, not just electrons).

The atomic number of an element is a fundamental property that uniquely identifies it and is equal to the number of protons in the nucleus.

Rutherford’s experiment provided evidence for a small, dense, positively charged nucleus. J.J. Thomson’s model was disproven by Rutherford’s findings. The number of electrons in a neutral atom is equal to the number of protons (the atomic number), but this is not the definition of mass number. The mass number is the sum of protons and neutrons, which account for most of the atom’s mass.

26. Which one of the following statements is correct?

Which one of the following statements is correct?

The image formed by a concave mirror for an object lying at infinity is at the principal focus, highly diminished, real and inverted.

A ray of light parallel to the principal axis after reflection from a concave mirror appears to diverge from the principal focus of the mirror.

The focal length of a spherical mirror is double of its radius of curvature.

A ray of light travelling from a rarer medium to a denser medium bends away from the normal.

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UPSC NDA-2 – 2015

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Let’s analyze each statement:
A) The image formed by a concave mirror for an object lying at infinity is indeed formed at the principal focus (F), is highly diminished (essentially a point image), and is real and inverted. This statement accurately describes the image formation for a concave mirror when the object is at infinity.

For a concave mirror, when an object is placed at infinity, the rays coming from it are parallel to the principal axis and converge at the principal focus after reflection, forming a real, inverted, and highly diminished image.

B) A ray parallel to the principal axis after reflection from a concave mirror passes *through* the principal focus, it does not appear to diverge from it. This description applies to a convex mirror.
C) The focal length (f) of a spherical mirror is half of its radius of curvature (R), i.e., f = R/2. The statement says it is double, which is incorrect.
D) A ray of light travelling from a rarer medium to a denser medium bends *towards* the normal, not away from it. Bending away from the normal occurs when light travels from a denser medium to a rarer medium.
Therefore, only statement A is correct.

27. In Egypt, ancient mummies can be found to have their arteries intact d

In Egypt, ancient mummies can be found to have their arteries intact due to well-preserved:

mineralized blood

fibroblasts fibre

elastic fibre

brown fat

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UPSC NDA-2 – 2015

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Ancient Egyptian mummification involved sophisticated techniques to preserve soft tissues. The structure and elasticity of arteries are largely due to the presence of elastic fibers within their walls. Effective embalming methods that preserved the protein structure of these elastic fibers would contribute significantly to the intactness of the arteries over millennia.

The structural integrity of arteries, including their elasticity, is primarily attributed to the presence of elastic fibers. Preservation of these fibers through mummification techniques helps keep the arteries intact.

Fibroblasts produce collagen and other matrix components, including the precursors of elastic fibers, but the mature elastic fiber itself provides the elasticity. Mineralized blood might refer to calcification or remnants within the vessel lumen, but it doesn’t explain the preservation of the vessel wall structure. Brown fat is a type of adipose tissue involved in thermogenesis and is not a structural component of arteries. Mummification processes often involved the removal of organs and treatment of tissues with various salts and resins to dehydrate them and inhibit microbial decay, preserving their structural components like elastic fibers.

28. The symbol of the element ‘Tungsten’ is:

The symbol of the element ‘Tungsten’ is:

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UPSC NDA-2 – 2015

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The chemical symbol for the element Tungsten is W. The symbol comes from its alternative name, Wolfram, which is derived from the mineral wolframite, a primary source of the element.

The chemical symbol W represents the element Tungsten, derived from the name Wolfram.

Let’s look at the other symbols provided:
A) Ta: Tantalum
C) Tl: Thallium
D) Tc: Technetium
Remembering the symbols for elements is fundamental in chemistry. Tungsten (W) is an important transition metal known for its high melting point.

29. Which one of the following pairs of properties of typical air masses i

Which one of the following pairs of properties of typical air masses is correct?

Maritime Equatorial: Warm oceans in the equatorial zone

Maritime Polar: Warm oceans in the tropical zone

Continental Tropical: Less warm oceans in the tropical zone

Continental Polar: Moist oceans in the polar zone

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UPSC NDA-2 – 2015

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Air masses are classified based on their source region’s latitude (determining temperature: Equatorial (E), Tropical (T), Polar (P), Arctic/Antarctic (A)) and the surface type (determining moisture: Maritime (m) over oceans, Continental (c) over land). A Maritime Equatorial air mass forms over warm oceans in the equatorial region, making it warm and moist.

Air masses are classified by temperature (based on latitude of origin) and moisture content (based on surface type of origin). Maritime Equatorial (mE) air masses originate over warm equatorial oceans.

Let’s examine the other options:
B) Maritime Polar (mP): Forms over cold oceans in polar regions, typically cold and moist. The description “Warm oceans in the tropical zone” refers to mT (Maritime Tropical).
C) Continental Tropical (cT): Forms over warm land in the tropics, typically warm and dry. The description “Less warm oceans in the tropical zone” is incorrect.
D) Continental Polar (cP): Forms over cold land in polar regions, typically cold and dry. The description “Moist oceans in the polar zone” refers to mP (Maritime Polar).
Only option A accurately describes the characteristics and source region of a Maritime Equatorial air mass.

30. X-rays are electromagnetic radiation whose wavelengths are of the orde

X-rays are electromagnetic radiation whose wavelengths are of the order of:

1 metre

10^-7 metre

10^-10 metre

10^-15 metre

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UPSC NDA-2 – 2015

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X-rays are a form of electromagnetic radiation with wavelengths ranging approximately from 10 picometers ($10^{-11}$ m) to 10 nanometers ($10^{-8}$ m). The option $10^{-10}$ metre falls squarely within this range.

X-rays occupy a position in the electromagnetic spectrum between ultraviolet radiation and gamma rays, characterized by wavelengths in the range of approximately $10^{-11}$ m to $10^{-8}$ m.

The electromagnetic spectrum spans a wide range of wavelengths and frequencies. Radio waves have wavelengths of metres to kilometres. Microwaves are around centimetres to metres. Infrared radiation is roughly from $7 \times 10^{-7}$ m to $10^{-3}$ m. Visible light is from $4 \times 10^{-7}$ m (violet) to $7 \times 10^{-7}$ m (red). Ultraviolet radiation is from $10^{-8}$ m to $4 \times 10^{-7}$ m. X-rays are from $10^{-11}$ m to $10^{-8}$ m. Gamma rays have wavelengths less than $10^{-12}$ m.