UPSC NDA-1

11. Which one of the following rivers was earlier known as “Vitasta” ?

Which one of the following rivers was earlier known as “Vitasta” ?

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Tista
Jhelum
Tungabhadra
Bharatpuzha
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The Jhelum River is one of the five major rivers of the Punjab region. In ancient Indian texts, particularly the Rigveda, this river was known by the name ‘Vitasta’. It is also mentioned as Hydaspes in ancient Greek texts, related to Alexander the Great’s Battle of the Hydaspes fought on its banks.
– Vitasta is the ancient Sanskrit name for the Jhelum River.
– The Jhelum River is a tributary of the Chenab, which flows into the Indus River.
– The Battle of the Hydaspes (Vitasta) was fought between Alexander the Great and King Porus.
The five rivers of Punjab are Jhelum (Vitasta), Chenab (Asikni), Ravi (Parushni/Iravati), Sutlej (Shatadru), and Beas (Vipasha). Their confluence forms the Panjnad, which joins the Indus River.

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12. Which one of the following is NOT a west flowing river ?

Which one of the following is NOT a west flowing river ?

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Periyar
Bharatpuzha
Pamba
Tamraparni
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Rivers in India are broadly classified based on where they drain their waters. West-flowing rivers flow into the Arabian Sea, while east-flowing rivers flow into the Bay of Bengal. Periyar, Bharatpuzha, and Pamba are all significant rivers flowing westward through the state of Kerala into the Arabian Sea. The Tamraparni River, however, flows eastward through Tamil Nadu and drains into the Gulf of Mannar (part of the Bay of Bengal).
– Periyar, Bharatpuzha, and Pamba are major west-flowing rivers of Kerala.
– Tamraparni is a major river of Tamil Nadu that flows eastward.
Most major rivers in the Deccan Plateau flow eastward into the Bay of Bengal because the general slope of the plateau is from west to east. Exceptions are a few large rivers like Narmada and Tapti, and many smaller rivers in the Western Ghats that flow westward.

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13. The equivalent weight of oxalic acid in C₂H₂O₄.2H₂O is

The equivalent weight of oxalic acid in C₂H₂O₄.2H₂O is

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45
63
90
126
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The formula given is for hydrated oxalic acid, C₂H₂O₄.2H₂O. Oxalic acid (C₂H₂O₄ or HOOC-COOH) is a diprotic acid, meaning it can donate two protons (H⁺). The equivalent weight of an acid is its molar mass divided by the number of acidic hydrogens that participate in the reaction (also called its basicity). In typical acid-base reactions, oxalic acid dihydrate reacts as a diprotic acid, donating both protons.
– The molar mass of C₂H₂O₄ = (2 × 12.01) + (2 × 1.01) + (4 × 16.00) = 24.02 + 2.02 + 64.00 = 90.04 g/mol.
– The molar mass of 2H₂O = 2 × (2 × 1.01 + 16.00) = 2 × 18.02 = 36.04 g/mol.
– The molar mass of C₂H₂O₄.2H₂O = 90.04 + 36.04 = 126.08 g/mol.
– Oxalic acid is a diprotic acid, meaning it has 2 acidic hydrogens.
– Equivalent weight = Molar mass / number of acidic hydrogens = 126.08 g/mol / 2 = 63.04 g/equivalent.
– Among the options, 63 is the closest value.
If the question were asking for the equivalent weight of *anhydrous* oxalic acid (C₂H₂O₄) reacting as a diprotic acid, the answer would be 90/2 = 45. If it reacted as a monoprotic acid, the equivalent weight would be 90 or 126 depending on whether anhydrous or hydrated form is considered as the basis for molar mass. However, the most common standard use of oxalic acid in volumetric analysis is as the dihydrate, reacting as a diprotic acid.

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14. Who among the following has explained the phenomenon of photo-electric

Who among the following has explained the phenomenon of photo-electric effect ?

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Max Planck
Albert Einstein
Neils Bohr
Ernest Rutherford
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The phenomenon of the photo-electric effect, where electrons are emitted from a metal surface when light shines on it, was explained by Albert Einstein in 1905. He proposed that light energy is quantized into discrete packets called photons and that the energy of each photon is proportional to its frequency (E = hf, based on Planck’s work). This revolutionary idea successfully explained the observed characteristics of the photo-electric effect, such as the existence of a threshold frequency and the dependence of emitted electron energy on the frequency of light, not its intensity.
– Max Planck introduced the concept of energy quantization (quanta).
– Albert Einstein applied the concept of light quanta (photons) to explain the photo-electric effect.
– Niels Bohr developed the quantum model of the atom.
– Ernest Rutherford discovered the atomic nucleus.
Einstein received the Nobel Prize in Physics in 1921 specifically for his services to Theoretical Physics, and especially for his discovery of the law of the photo-electric effect. This work was crucial in the development of quantum mechanics.

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15. Dinitrogen (N₂) and dioxygen (O₂) are the main constituents of air but

Dinitrogen (N₂) and dioxygen (O₂) are the main constituents of air but they do not react with each other to form oxides of nitrogen because

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the reaction requires initiation by a catalyst
oxides of nitrogen are unstable
the reaction is endothermic and requires very high temperature
the stoichiometry of N₂ and O₂ in air is not ideal for the reaction to take place
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Dinitrogen (N₂) and dioxygen (O₂) molecules are very stable due to strong bonds (triple bond in N₂, double bond in O₂). The reaction between them to form oxides of nitrogen, such as nitric oxide (NO), is highly endothermic (requires energy input) and has a high activation energy barrier. Therefore, this reaction requires very high temperatures (e.g., found in lightning strikes or internal combustion engines) to proceed significantly. At normal atmospheric temperatures, there isn’t enough energy to break the strong N≡N bond and initiate the reaction.
– The reaction N₂ + O₂ → 2NO is endothermic (ΔH > 0).
– The strong triple bond in N₂ requires a large amount of energy to break.
– Standard atmospheric temperatures are insufficient to overcome the activation energy barrier for this reaction.
While a catalyst could potentially lower the activation energy, the primary reason the reaction doesn’t occur spontaneously in the air is the high energy requirement. Oxides of nitrogen, once formed, vary in stability, but their stability is not the reason for their lack of formation under normal conditions. The stoichiometry in air is about 4:1 N₂:O₂, which is not ideal for NO formation (1:1), but this ratio doesn’t prevent the reaction from occurring at all; it just affects equilibrium yield.

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16. Which one of the following is an organic acid ?

Which one of the following is an organic acid ?

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Hydrochloric acid
Nitric acid
Acetic acid
Sulphuric acid
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Organic acids are typically organic compounds that contain acidic properties. The most common type of organic acid is a carboxylic acid, which contains a carboxyl group (-COOH). Among the given options, Acetic acid (CH₃COOH) is an organic compound containing a carboxyl group and is therefore an organic acid.
– Hydrochloric acid (HCl) is a strong inorganic acid (mineral acid).
– Nitric acid (HNO₃) is a strong inorganic acid (mineral acid).
– Acetic acid (CH₃COOH) is a carboxylic acid and a weak organic acid. It is the main component of vinegar.
– Sulphuric acid (H₂SO₄) is a strong inorganic acid (mineral acid).
Inorganic acids are typically derived from inorganic compounds and often do not contain carbon (with a few exceptions like carbonic acid, H₂CO₃). Organic acids are carbon-based compounds, typically derived from living organisms or their products.

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17. Which one of the following statements is NOT correct for the given rea

Which one of the following statements is NOT correct for the given reaction ? Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)

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Iron is the reducing agent
The solution turns green in colour after the reaction
Copper is a more reactive metal than iron
The reaction is an example of a redox reaction
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The reaction shown is a single displacement reaction where iron (Fe) displaces copper (Cu) from copper sulphate (CuSO₄) solution: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s). This occurs because iron is more reactive than copper. In the reactivity series of metals, a more reactive metal can displace a less reactive metal from its salt solution.
– Statement A is correct: Iron (oxidation state 0) is oxidized to Fe²⁺ (oxidation state +2) by losing electrons. A substance that causes reduction by being oxidized itself is called a reducing agent.
– Statement B is correct: Copper sulphate solution is typically blue in colour. Iron(II) sulphate (FeSO₄) solution, formed after the reaction, is green in colour. So, the solution’s colour changes from blue to green.
– Statement C is incorrect: The displacement of copper by iron indicates that iron is more reactive than copper. Copper is less reactive than iron.
– Statement D is correct: Iron is oxidized (Fe → Fe²⁺) and copper ions are reduced (Cu²⁺ → Cu). Reactions involving both oxidation and reduction are called redox reactions.
The reactivity series of metals (partially): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. A metal higher in the series can displace a metal lower in the series from its salt solution.

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18. Basic scientific principle behind a nuclear reactor is

Basic scientific principle behind a nuclear reactor is

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Nuclear fusion
Controlled nuclear fusion
Uncontrolled nuclear fission
Controlled nuclear fission
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The correct answer is (D) Controlled nuclear fission.
Nuclear reactors generate energy by splitting heavy atomic nuclei, such as Uranium-235, in a process called nuclear fission. This process releases a large amount of energy, neutrons, and other particles.
In a nuclear reactor, the fission chain reaction is carefully controlled using materials like control rods (which absorb neutrons) and moderators (which slow down neutrons) to ensure a sustained but non-explosive release of energy. This controlled reaction differentiates a nuclear reactor from an atomic bomb, which relies on an uncontrolled chain reaction (uncontrolled nuclear fission). Nuclear fusion, the process of combining light nuclei, is the principle behind the sun’s energy and thermonuclear weapons, but it is not yet used for commercial power generation in current nuclear reactors due to the extremely high temperatures and pressures required.

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19. Let us consider a copper wire having radius r and length l. Let its re

Let us consider a copper wire having radius r and length l. Let its resistance be R. If the radius of another copper wire is 2r and the length is l/2 then the resistance of this wire will be

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R
2R
R/4
R/8
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The correct answer is (D) R/8.
The resistance (R) of a wire is directly proportional to its length (l) and inversely proportional to its cross-sectional area (A). The formula is R = ρ(l/A), where ρ is the resistivity of the material. The cross-sectional area of a wire with radius r is A = πr².
Let the initial resistance be R. R = ρ * (l / (πr²)).
For the second wire, the radius is r’ = 2r and the length is l’ = l/2.
The new cross-sectional area A’ = π(r’)² = π(2r)² = π(4r²) = 4πr².
The new resistance R’ = ρ * (l’ / A’) = ρ * ((l/2) / (4πr²)).
R’ = ρ * (l / (8πr²)) = (1/8) * [ρ * (l / (πr²))].
Since R = ρ * (l / (πr²)), we have R’ = R/8.

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20. Which one of the following could be the melting point of iron ?

Which one of the following could be the melting point of iron ?

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25°C
37°C
500°C
1500°C
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The correct answer is (D) 1500°C.
The melting point of pure iron is approximately 1538°C (2800°F). The melting points of common metals are relatively high compared to typical ambient temperatures.
Options (A) 25°C and (B) 37°C are typical room and body temperatures, far too low for the melting point of a metal like iron. Option (C) 500°C is also too low; this might be closer to the melting point of certain alloys or other materials, but not iron. Option (D) 1500°C falls within the correct range for the melting point of iron. Steel, an alloy of iron and carbon, has a melting point that is typically lower than pure iron but still in the range of 1370–1530 °C, depending on the composition.

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