UPSC NDA-1

11. The Poisonous nature of Carbon monoxide (CO) is due to its

The Poisonous nature of Carbon monoxide (CO) is due to its

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insolubility in water
ability to form a complex with haemoglobin
ability to reduce some metal oxides
property of having one sigma bond
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UPSC NDA-1 – 2018
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The poisonous nature of carbon monoxide (CO) is primarily due to its ability to bind strongly to haemoglobin in red blood cells.
Carbon monoxide has a much higher affinity for haemoglobin (about 200-250 times greater) than oxygen. When inhaled, CO binds to haemoglobin forming carboxyhaemoglobin (COHb), effectively reducing the capacity of the blood to transport oxygen. This leads to oxygen deprivation in the body’s tissues and organs.
Symptoms of carbon monoxide poisoning include headache, dizziness, nausea, weakness, confusion, and in severe cases, unconsciousness, coma, and death. CO is produced by the incomplete combustion of carbon-containing materials.

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12. Which one of the following is the purest form of Carbon ?

Which one of the following is the purest form of Carbon ?

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Charcoal
Coke
Fullerene
Carbon black
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UPSC NDA-1 – 2018
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Among the given options, Fullerene is considered one of the purest forms of carbon because it consists of distinct molecules made solely of carbon atoms, which can be isolated and purified.
Charcoal, coke, and carbon black are amorphous or paracrystalline forms of carbon often produced by incomplete combustion or carbonization of organic matter. They typically contain impurities and consist of irregular aggregates of carbon structures. Fullerenes, like C₆₀, are molecular allotropes with cage-like structures composed only of carbon atoms, and they can be synthesized and purified to a high degree.
Other very pure forms of carbon include diamond (a crystalline allotrope) and carbon nanotubes and graphene (which can be produced with very high purity). Among the options listed, Fullerene best fits the description of a pure form.

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13. Which one of the following properties is NOT true for graphite ?

Which one of the following properties is NOT true for graphite ?

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Hybridisation of each carbon atom is sp³
Hybridisation of each carbon atom is sp²
Electrons are delocalized over the whole sheet of atoms
Each layer is composed of hexagon rings
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The statement that the hybridisation of each carbon atom in graphite is sp³ is NOT true.
Graphite has a layered structure. Each carbon atom within a layer is bonded to three other carbon atoms in a hexagonal lattice. These three bonds are formed using sp² hybrid orbitals. The remaining unhybridized p-orbital on each carbon atom overlaps with adjacent p-orbitals, creating a delocalized pi electron system across the layer. sp³ hybridization occurs in diamond, where each carbon atom forms single bonds with four other carbon atoms in a tetrahedral structure.
The delocalized electrons in graphite layers allow it to conduct electricity. The layers are held together by weak van der Waals forces, which explains its softness and use as a lubricant.

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14. How is carbon black obtained ?

How is carbon black obtained ?

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By heating wood at high temperature in absence of air
By heating coal at high temperature in absence of air
By burning hydrocarbons in a limited supply of air
By heating coal at high temperature in presence of air
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UPSC NDA-1 – 2018
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Carbon black is obtained by the incomplete combustion or thermal decomposition of hydrocarbons in a limited supply of air.
Methods like the furnace black process or channel black process involve burning hydrocarbon feedstock (like natural gas or oil) with insufficient oxygen, leading to the formation of fine carbon particles (soot), which is collected as carbon black.
Heating wood or coal at high temperatures in the absence of air are processes like pyrolysis or carbonization, which yield charcoal and coke, respectively. These are different forms of carbon and processes.

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15. Which one of the following is the number of water molecules that share

Which one of the following is the number of water molecules that share with two formula unit CaSO₄ in plaster of Paris ?

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One
Two
Five
Ten
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UPSC NDA-1 – 2018
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In plaster of Paris (CaSO₄ · ½ H₂O), one formula unit of CaSO₄ is associated with half a molecule of water. Therefore, two formula units of CaSO₄ share one molecule of water (2 * ½ H₂O = 1 H₂O).
Plaster of Paris is calcium sulfate hemihydrate (CaSO₄ · ½ H₂O). This chemical formula indicates the ratio of calcium sulfate to water molecules in the crystal structure.
When plaster of Paris is mixed with water, it rehydrates to form gypsum (CaSO₄ · 2H₂O), a hard solid. This process is exothermic and is the basis for its use in casting and construction.

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16. Which one of the following devices is used to measure atmospheric pres

Which one of the following devices is used to measure atmospheric pressure ?

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Ammeter
Barometer
Potentiometer
Lactometer
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UPSC NDA-1 – 2018
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A barometer is the device specifically used to measure atmospheric pressure.
Atmospheric pressure is the pressure exerted by the weight of the air column above a point on Earth’s surface. Devices like mercury barometers (Torricelli’s principle) or aneroid barometers are designed to measure this pressure.
An ammeter measures electric current. A potentiometer measures electrical potential difference (voltage). A lactometer is a hydrometer used to test the purity or density of milk.

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17. Which of the following statements about a fluid at rest in a cup is/ar

Which of the following statements about a fluid at rest in a cup is/are correct ?

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  • 1. Pressure is same at all the points in the fluid.
  • 2. Pressure is exerted on the walls.
  • 3. Pressure exists everywhere in the fluid.

Select the correct answer using the code given below :

1 and 2 only
2 and 3 only
1 only
1, 2 and 3
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Statements 2 and 3 are correct regarding a fluid at rest in a cup. Statement 1 is incorrect as pressure varies with depth.
In a fluid at rest, pressure is exerted on any surface in contact with the fluid (like the walls of the cup) and acts perpendicular to the surface. Pressure also exists throughout the fluid’s volume. However, pressure in a fluid at rest varies with depth due to the weight of the fluid above, according to the formula P = P₀ + ρgh, where P₀ is the surface pressure, ρ is the fluid density, g is gravity, and h is depth. Thus, pressure is not the same at all points unless they are at the same depth.
Pressure in a fluid at rest is the same at all points at the same horizontal level. Pascal’s law states that pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and the walls of the containing vessel.

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18. A ball balanced on a vertical rod is an example of

A ball balanced on a vertical rod is an example of

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stable equilibrium
unstable equilibrium
neutral equilibrium
perfect equilibrium
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A ball balanced precisely on a vertical rod is in unstable equilibrium.
– In unstable equilibrium, if the object is slightly displaced from its equilibrium position, it will move further away from that position.
– A ball balanced on a pointed object or the crest of a curve represents a point of unstable equilibrium. Any tiny disturbance will cause it to fall.
– Stable equilibrium occurs when a slight displacement causes the object to return to its original position (e.g., a ball in the bottom of a bowl).
– Neutral equilibrium occurs when a slight displacement causes the object to remain in its new position (e.g., a ball on a flat surface).

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19. Which one of the following statements about the mass of a body is corr

Which one of the following statements about the mass of a body is correct ?

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It changes from one place to another
It is same everywhere
It depends on its shape
It does not depend on its temperature
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UPSC NDA-1 – 2018
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Statement B is correct. Mass is a fundamental property of a body that represents the amount of matter it contains. It is an intrinsic property and remains the same regardless of the body’s location (where gravity varies) or its shape.
– Mass is distinct from weight, which is the force of gravity acting on a mass and therefore changes with location.
– Mass is invariant under changes in location, shape, or phase (in a classical context).
Statement A is incorrect as it describes weight, not mass. Statement C is incorrect; mass depends on the amount of matter, not its arrangement (shape). Statement D is also correct in a classical physics context, as temperature changes (which represent changes in internal energy) cause only negligible changes in mass according to E=mc^2, which are typically ignored unless dealing with nuclear reactions or extremely high energies. However, B is a more fundamental and universally applicable definition when comparing mass to variables like location. Since only one option can be chosen, B is the most definitive correct statement about mass.

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20. Which of the following statements about latent heat for a given substa

Which of the following statements about latent heat for a given substance is/are correct ?

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  • 1. It is fixed at a given temperature.
  • 2. It depends upon the temperature and volume.
  • 3. It is independent of temperature and volume.
  • 4. It depends on the temperature but independent of volume.

Select the correct answer using the code given below :

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2
1 and 3
4 only
1 and 4
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Statement 1 is correct: For a specific substance at a given pressure, the latent heat associated with a phase transition (like melting or boiling) is fixed at the transition temperature. Statement 4 is also considered correct in the context that the value of latent heat is characteristic of the specific transition temperature, though the phrasing “depends on the temperature” can be ambiguous.
– Latent heat is the energy absorbed or released during a phase change at constant temperature and pressure.
– Statement 1 accurately reflects that for a specific phase transition at standard conditions, the latent heat value is constant at the transition temperature.
– While the phase change occurs *at* a constant temperature, the *value* of the latent heat can technically vary with the pressure, which in turn affects the transition temperature. Statement 4 might be interpreting “depends on the temperature” as being specific to the transition temperature value, and “independent of volume” in the sense that the volume of the substance isn’t a variable determining the latent heat value itself, unlike say, specific heat capacity which can be defined at constant volume.
Statement 2 is incorrect as volume is not a primary variable defining latent heat. Statement 3 is incorrect as latent heat is fundamentally linked to the transition temperature. Given the options, 1 and 4 are the most plausible correct statements, despite the awkward phrasing of 4. This suggests that the question setter considered both 1 and 4 as correct representations, with 4 perhaps indicating dependence on the *specific transition temperature*.

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