UPSC NDA-1

41. Solder is an alloy of

Solder is an alloy of

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Cu and Sn.
Fe and Zn.
Pb and Sn.
Ag and Zn.
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Solder is typically an alloy of lead (Pb) and tin (Sn).
Traditional solder, widely used for joining metals in plumbing and electronics, is an alloy primarily composed of lead and tin. The ratio of lead to tin affects the melting point and properties of the solder. Common compositions include 60% tin and 40% lead, or the eutectic alloy of 63% tin and 37% lead which has the lowest melting point.
Due to environmental concerns about lead toxicity, lead-free solders have become increasingly popular, especially in electronics. Lead-free solders often consist mainly of tin alloyed with other metals like silver (Ag), copper (Cu), and sometimes bismuth (Bi) or antimony (Sb). However, without specifying “lead-free”, the standard Pb-Sn alloy is implied.

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42. In electrolytic refining of copper, the electrolyte is a solution of

In electrolytic refining of copper, the electrolyte is a solution of

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acidified copper chloride.
acidified copper sulphate.
potassium chloride.
sodium sulphate.
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In electrolytic refining of copper, the electrolyte is a solution of acidified copper sulphate.
In the process of electrolytic refining, impure copper acts as the anode and dissolves as Cu²⁺ ions, while pure copper acts as the cathode where Cu²⁺ ions from the electrolyte are deposited. The electrolyte needs to contain Cu²⁺ ions, which is achieved by using a solution of copper sulfate (CuSO₄). Sulfuric acid (H₂SO₄) is added to the copper sulfate solution to increase its conductivity and prevent the precipitation of copper hydroxide.
Impurities in the anode that are less reactive than copper (like gold, silver, platinum) settle down as anode mud, while more reactive impurities (like zinc, iron, nickel) dissolve in the electrolyte but do not get deposited on the cathode under controlled voltage.

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43. Which one of the following is not used as a raw material in the manufa

Which one of the following is not used as a raw material in the manufacture of glass ?

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Soda
Alumina
Borax
Gypsum
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Gypsum is not typically used as a primary raw material in the manufacture of standard glass.
The main raw materials for manufacturing common soda-lime glass are silica (sand), soda ash (sodium carbonate), and limestone (calcium carbonate). Alumina and borax are used in the production of specialized glasses like aluminosilicate glass and borosilicate glass, respectively. Gypsum (calcium sulfate) is primarily used in plaster, drywall, and cement production.
Minor components might be added to glass batches as fining agents (to remove bubbles), colorants, or flux enhancers, but gypsum is not a standard ingredient for bulk glass manufacturing.

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44. The composition of gases in exosphere is

The composition of gases in exosphere is

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Helium and Hydrogen.
Neon and Oxygen.
Neon and Hydrogen.
Helium and Neon.
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The composition of gases in the exosphere is primarily Helium and Hydrogen.
The exosphere is the uppermost layer of Earth’s atmosphere. At these extremely high altitudes, the atmosphere is very thin, and the lightest gases, mainly hydrogen and helium, are the most abundant because gravity has less hold on them, and they can even escape into outer space.
Below the exosphere is the thermosphere, where lighter gases become increasingly dominant with altitude, but oxygen and nitrogen are still significant at lower thermospheric levels. In the exosphere, the gases are so sparse that particles travel long distances without colliding.

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45. Which one of the following is the chemical formula of Hypobromous acid

Which one of the following is the chemical formula of Hypobromous acid ?

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HBrO₄
HOBr
HBr
HBrO₃
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The chemical formula of Hypobromous acid is HOBr.
Hypobromous acid is a weak acid with the chemical formula HOBr or HBrO. It belongs to the group of hypohalous acids (HOX, where X is a halogen).
The other options represent different bromine oxyacids:
– HBrO₄ is perbromic acid (bromine in +7 oxidation state).
– HBr is hydrogen bromide (hydrobromic acid).
– HBrO₃ is bromic acid (bromine in +5 oxidation state).
In HOBr, bromine is in the +1 oxidation state.

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46. The statement “friction force is a contact force while magnetic force

The statement “friction force is a contact force while magnetic force is a non-contact force” is

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always true.
true only at 0°C.
a false statement.
either true or false depending upon the temperature of the surroundings.
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The statement “friction force is a contact force while magnetic force is a non-contact force” is always true.
Contact forces arise from the physical contact between objects (e.g., friction, normal force). Non-contact forces (also known as field forces) act between objects even when they are not in physical contact (e.g., gravitational force, magnetic force, electrostatic force). Friction requires surfaces to be in contact, while magnetic forces act through a magnetic field, regardless of contact.
This distinction between contact and non-contact forces is a fundamental concept in classical mechanics. Temperature or surrounding conditions do not alter the inherent nature of these forces in this classification.

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47. LED (a semi-conductor device) is an abbreviation that stands for

LED (a semi-conductor device) is an abbreviation that stands for

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Licence for Energy Detector.
Light Energy Device.
Light Emitting Diode.
Lost Energy Detector.
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LED stands for Light Emitting Diode.
A Light Emitting Diode (LED) is a semiconductor device that emits light when an electric current passes through it. This effect is a form of electroluminescence.
LEDs are widely used in various applications, including indicator lights, displays, lighting, and backlighting for screens, due to their energy efficiency, longevity, and compact size.

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48. Which of the following pairs of physical phenomenon and the discoverer

Which of the following pairs of physical phenomenon and the discoverer is/are correctly matched ?

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1. James Chadwick : Photoelectric effect
2. Albert Einstein : Neutron
3. Marie Curie : Radium

Select the correct answer using the code given below :

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1, 2 and 3
1 and 2 only
2 and 3 only
3 only
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Only the third pair is correctly matched.
– James Chadwick discovered the neutron in 1932. The photoelectric effect was explained by Albert Einstein in 1905, building on observations by Heinrich Hertz.
– Albert Einstein is famous for his theory of relativity and his explanation of the photoelectric effect, not the discovery of the neutron.
– Marie Curie, along with her husband Pierre Curie, discovered the elements polonium and radium in 1898.
Marie Curie was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first woman to win a Nobel Prize, the first person and only woman to win the Nobel Prize twice, and the only person to win the Nobel Prize in two different scientific fields.

49. Which one of the following regarding density of water at atmospheric p

Which one of the following regarding density of water at atmospheric pressure is correct ?

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Density of water at 4°C is 1000 kg/m³.
Density of water at 0°C is 1000 kg/m³.
Density of water at 0°C is 100 kg/m³.
Density of water at 4°C is 10 kg/m³.
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Density of water at atmospheric pressure is maximum at 4°C, and its value is approximately 1000 kg/m³.
Water exhibits anomalous expansion; its density increases from 0°C to 4°C, where it reaches its maximum density, and then decreases as the temperature rises above 4°C. At 0°C, water is less dense than at 4°C (whether in liquid or solid state).
The density of water at 0°C (liquid) is about 999.84 kg/m³, and the density of ice at 0°C is about 916.7 kg/m³. The value 1000 kg/m³ is a commonly used approximation for the density of liquid water at 4°C and is equivalent to 1 g/cm³.

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50. Consider the following statements about Light year : Light year is

Consider the following statements about Light year :

  • Light year is a unit for measurement of very large distances.
  • Light year is a unit for measurement of very large time intervals.
  • Light year is a unit for measurement of intensity of light.

Which of the statements given above is/are correct ?

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1, 2 and 3
2 and 3 only
1 and 2 only
1 only
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Statement 1 is correct, while statements 2 and 3 are incorrect. A light-year is a unit of distance.
A light-year is defined as the distance that light travels in vacuum in one Julian year (365.25 days). It is used to measure very large distances, particularly in astronomy.
The approximate value of a light-year is 9.461 × 10¹⁵ meters or 63,241 astronomical units (AU). Other units of astronomical distance include the astronomical unit (AU) and the parsec (pc). The parsec is defined based on parallax and is approximately 3.26 light-years.

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