UPSC NDA-2

41. Vapours of sulphur escaping from a volcano often form a crust on the r

Vapours of sulphur escaping from a volcano often form a crust on the rocks. The process involved is an example of

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condensation
precipitation
deposition
evaporation
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The correct answer is deposition.
Deposition is the phase transition in which gas transforms into solid without passing through the liquid phase. Sulphur escaping from a volcano as vapour (gas) cools upon contact with rocks and directly forms a solid crust. This is the reverse of sublimation.
Condensation is the change of state from gas to liquid. Precipitation is the process of forming a solid from a solution or vapour phase, often used for meteorological phenomena (rain, snow, etc.) or chemical solid formation from a liquid. Evaporation is the change of state from liquid to gas.

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42. The number of structural isomers of pentane is

The number of structural isomers of pentane is

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5
4
2
3
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The correct answer is 3.
Structural isomers are compounds with the same molecular formula but different arrangements of atoms. Pentane has the molecular formula C₅H₁₂. The three structural isomers of pentane are:
1. n-pentane (a straight chain of five carbon atoms).
2. Isopentane (2-methylbutane, a four-carbon chain with a methyl group attached to the second carbon).
3. Neopentane (2,2-dimethylpropane, a three-carbon chain with two methyl groups attached to the central carbon).
As the number of carbon atoms increases in alkanes, the number of possible structural isomers grows rapidly. For example, hexane (C₆H₁₄) has 5 isomers, and heptane (C₇H₁₆) has 9 isomers.

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43. Liquid vegetable oils are converted to solid margarine by the use of

Liquid vegetable oils are converted to solid margarine by the use of

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hydrogen gas
chlorine gas
carbon dioxide gas
oxygen gas
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The correct answer is hydrogen gas.
Liquid vegetable oils are typically unsaturated fats, meaning they contain carbon-carbon double bonds. To convert these liquid oils into solid or semi-solid fats like margarine, hydrogen gas is added across the double bonds in the presence of a catalyst (usually nickel, palladium, or platinum). This process is called hydrogenation.
Partial hydrogenation can lead to the formation of trans fats, which have been linked to negative health effects. Modern hydrogenation processes aim to minimize trans fat formation while achieving the desired consistency.

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44. Bee sting leaves an acid which causes pain and irritation. The acid re

Bee sting leaves an acid which causes pain and irritation. The acid released is

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tartaric acid
citric acid
ethanoic acid
methanoic acid
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The correct answer is methanoic acid.
Bee sting venom contains several substances, including formic acid, which is also known as methanoic acid (HCOOH). This acid is primarily responsible for the pain and irritation experienced from a bee sting.
While bee venom contains various components, including peptides and enzymes, formic acid is the key acidic component causing the immediate stinging sensation. Wasp stings, in contrast, are alkaline.

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45. Which one of the following salts does not possess water of

Which one of the following salts does not possess water of crystallization?

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Potassium permanganate
Blue vitriol
Washing soda
Mohr's salt
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The correct answer is Potassium permanganate.
Salts that do not possess water of crystallization are called anhydrous salts. Among the given options, Potassium permanganate (KMnO₄) is typically an anhydrous salt. Blue vitriol (CuSO₄·5H₂O), Washing soda (Na₂CO₃·10H₂O), and Mohr’s salt ((NH₄)₂Fe(SO₄)₂·6H₂O) are common examples of hydrated salts, meaning they contain a fixed number of water molecules (water of crystallization) associated with their crystal structure.
Water of crystallization is water that is stoichiometrically bound into a crystal. It is necessary for the maintenance of the crystalline properties but can usually be removed by heating, resulting in the anhydrous salt.

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46. Bronze is an alloy of

Bronze is an alloy of

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Cu and Zn
Cu and Sn
Zn and Mg
Fe and Cu
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Bronze is an alloy of copper (Cu) and tin (Sn).
Alloys are mixtures of metals, or a mixture of a metal and another element. Bronze is historically significant and known for its hardness and durability.
Common metal alloys include:
– Brass: Copper (Cu) and Zinc (Zn)
– Bronze: Copper (Cu) and Tin (Sn)
– Stainless Steel: Iron (Fe), Chromium (Cr), Nickel (Ni), and Carbon (C)
– Solder: Tin (Sn) and Lead (Pb)

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47. Which one of the following statements about speed and velocity is

Which one of the following statements about speed and velocity is correct?

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Speed and velocity both are vector quantities.
Speed and velocity both are scalar quantities.
Speed is vector quantity and velocity is scalar quantity.
Speed is scalar quantity and velocity is vector quantity.
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Speed is a scalar quantity and velocity is a vector quantity.
– **Speed** is the magnitude of how fast an object is moving. It only has magnitude and no direction. Quantities with magnitude only are called scalar quantities.
– **Velocity** is the rate of change of displacement. It has both magnitude (speed) and direction. Quantities with both magnitude and direction are called vector quantities.
For example, saying a car is travelling at “50 km/h” describes its speed (a scalar). Saying a car is travelling at “50 km/h North” describes its velocity (a vector).

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48. The presence of magnetic field can be determined using which one of th

The presence of magnetic field can be determined using which one of the following instruments?

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Ammeter
Voltmeter
Magnetic needle
Motor
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The presence of a magnetic field can be determined using a magnetic needle.
A magnetic needle, like the one in a compass, is a small magnet pivoted to rotate freely. When placed in a magnetic field, it aligns itself with the direction of the field lines, indicating the presence and direction of the field.
An Ammeter measures electric current. A Voltmeter measures electric potential difference (voltage). A Motor converts electrical energy into mechanical energy using the principle of magnetic force on a current-carrying wire, but it’s not primarily an instrument for *detecting* a magnetic field’s presence in general. Other instruments for measuring magnetic fields include magnetometers, but a magnetic needle is a simple and fundamental tool for detection.

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49. A DC generator works on the principle of

A DC generator works on the principle of

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Ohm's law
Joule's law of heating
Faraday's laws of electromagnetic induction
None of the above
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A DC generator works on the principle of Faraday’s laws of electromagnetic induction.
Electromagnetic induction is the process where a conductor moving through a magnetic field (or a changing magnetic field near a conductor) induces an electromotive force (EMF), which can drive an electric current. Faraday’s laws quantify this phenomenon.
A generator utilizes mechanical energy (to rotate a coil or magnetic field) to cause a change in magnetic flux through a coil, thereby inducing an electric current according to Faraday’s laws. Ohm’s law relates voltage, current, and resistance in a circuit. Joule’s law of heating describes the heat produced by current flowing through a resistor. A motor works on the principle of the force experienced by a current-carrying conductor in a magnetic field.

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50. A current of 0·6 A is drawn by an electric bulb for 10 minutes. Which

A current of 0·6 A is drawn by an electric bulb for 10 minutes. Which one of the following is the amount of electric charge that flows through the circuit?

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6 C
0·6 C
360 C
36 C
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The amount of electric charge that flows through the circuit is 360 C.
Electric charge (Q) is defined as the product of electric current (I) and time (t): Q = I × t.
The current given is I = 0.6 A.
The time given is t = 10 minutes. This needs to be converted to seconds: 10 minutes × 60 seconds/minute = 600 seconds.
Now, calculate the charge: Q = 0.6 A × 600 s = 360 Ampere-seconds. The unit of electric charge is the Coulomb (C), where 1 Coulomb = 1 Ampere × 1 second. Therefore, Q = 360 C.

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