UPSC CDS-1 Archives

1. Methanoic acid is normally found in :

Methanoic acid is normally found in :

muscles

urine

ant stings

human brain

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

Methanoic acid (formic acid, HCOOH) is notably found in the venom of ants and in the stinging hairs of nettles. It is injected when an ant bites or when contact is made with a nettle, causing pain and irritation.

Methanoic acid is the simplest carboxylic acid. Its historical name, formic acid, comes from the Latin word “formica,” meaning ant, due to its initial isolation from ants.

Lactic acid is found in muscles (formed during anaerobic respiration). Urine contains urea and other waste products. The human brain contains various complex organic molecules, including neurotransmitters and lipids, but methanoic acid is not a primary constituent.

2. Which one of the following is not an example of an oxidation reaction

Which one of the following is not an example of an oxidation reaction ?

The taste of butter changes if left for a longer period

A white substance is formed when an aqueous solution of barium chloride is mixed with sodium sulphate solution

A reddish-brown powder gets coated on articles made of iron

Wine gets sour with time

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

The reaction where a white substance (BaSO4) is formed when barium chloride solution is mixed with sodium sulphate solution is a double displacement reaction (precipitation). In this type of reaction, ions are exchanged between two compounds, but there is typically no change in the oxidation states of the elements involved, meaning it is not an oxidation-reduction (redox) reaction.

Oxidation is a chemical process involving the loss of electrons, gain of oxygen, or loss of hydrogen. Redox reactions involve both oxidation and reduction. Precipitation reactions, where insoluble salts form from the mixing of solutions, are generally non-redox reactions if the oxidation states of the ions remain unchanged.

A) Rancidity of butter is due to oxidation of fats. C) Rusting of iron involves the oxidation of iron. D) Wine turning sour (acetification) is the oxidation of ethanol to acetic acid. These are all examples of oxidation reactions (specifically, redox processes). The reaction BaCl2(aq) + Na2SO4(aq) -> BaSO4(s) + 2NaCl(aq) is a pure double displacement (precipitation) reaction without electron transfer between reacting species.

3. The number of moles of oxygen gas used in the complete combustion of 1

The number of moles of oxygen gas used in the complete combustion of 1 mole of glucose is :

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

The balanced chemical equation for the complete combustion of glucose (C6H12O6) shows that 1 mole of glucose reacts with 6 moles of oxygen gas (O2).

Complete combustion of a hydrocarbon or carbohydrate involves reaction with sufficient oxygen to produce carbon dioxide (CO2) and water (H2O). Balancing the chemical equation ensures that the number of atoms of each element is the same on both the reactant and product sides, representing the stoichiometric ratios.

The balanced combustion reaction for glucose is: C6H12O6(s) + 6O2(g) -> 6CO2(g) + 6H2O(l). From this equation, the molar ratio of glucose to oxygen is 1:6. Therefore, 1 mole of glucose requires 6 moles of oxygen gas for complete combustion.

4. What happens to the gravitational force between two objects if the mas

What happens to the gravitational force between two objects if the mass of one object is doubled and the distance between them is also doubled ?

The force would remain the same

The force would be doubled

The force would be halved

The force would increase by a factor of 4

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

According to Newton’s Law of Gravitation, the force is directly proportional to the product of the masses and inversely proportional to the square of the distance between them. Doubling one mass increases the force by a factor of 2. Doubling the distance increases the distance squared by a factor of 4 (2^2), which decreases the force by a factor of 4. The combined effect is a force that is (2 * 1) / 4 = 1/2 times the original force.

Newton’s Law of Gravitation is given by F = G * (m1 * m2) / r^2, where F is the gravitational force, G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between their centers.

If the mass of one object is doubled (m1′ = 2m1) and the distance is doubled (r’ = 2r), the new force F’ is given by F’ = G * (m1′ * m2) / (r’)^2 = G * (2m1 * m2) / (2r)^2 = G * (2m1 * m2) / (4r^2) = (2/4) * G * (m1 * m2) / r^2 = (1/2) * F. Thus, the force would be halved.

5. A boy completes one round of a circular track of diameter 200 m in 30

A boy completes one round of a circular track of diameter 200 m in 30 s. What will be the displacement at the end of 3 minutes and 45 seconds ?

50 m

100 m

200 m

236 m

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

The boy completes 7.5 rounds in 3 minutes and 45 seconds. After 7 complete rounds, the displacement is zero. The displacement after the remaining 0.5 rounds (half a round) is the straight-line distance between the starting point and the diametrically opposite point. This distance is equal to the diameter of the circular track.

Displacement is a vector quantity defined as the shortest straight-line distance between the initial and final positions. In circular motion, after completing one or more full rounds, the displacement is zero because the final position is the same as the initial position. After half a round, the final position is diametrically opposite the initial position.

The diameter of the track is 200 m, so the radius is 100 m. The time taken for one round is 30 s. Total time = 3 minutes 45 seconds = 180 + 45 = 225 s. Number of rounds = Total time / Time per round = 225 s / 30 s = 7.5. Displacement after 7.5 rounds is the same as displacement after 0.5 rounds. The starting point and the point diametrically opposite are separated by the diameter, which is 200 m.

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

Which one of the following statements is not correct ?

An electric motor converts electrical energy into mechanical energy.

An electric generator works on the principle of electromagnetic induction.

The magnetic field at the centre of a long circular coil carrying current will be parallel straight lines.

A wire with a green insulation is usually the live wire of an electric supply.

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

Statement D is incorrect because a wire with green (or green/yellow) insulation is typically the earth wire in an electric supply, not the live wire.

Standard electrical wiring colour codes are used to identify the different wires in a circuit: Live, Neutral, and Earth. These colours vary by region, but green or green/yellow is almost universally used for the Earth wire, while red or brown is common for the Live wire, and black or blue is common for the Neutral wire.

Statement A is correct as electric motors convert electrical energy into mechanical energy using the force on a current-carrying conductor in a magnetic field. Statement B is correct as electric generators produce electric current based on the principle of electromagnetic induction, where a changing magnetic field induces an electric current. Statement C is correct; inside a long circular coil (solenoid) carrying current, the magnetic field lines are parallel straight lines, indicating a uniform field.

7. At the time of short-circuit, the current in the circuit :

At the time of short-circuit, the current in the circuit :

reduces substantially.

does not change.

increases heavily.

keeps on fluctuating.

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

A short-circuit occurs when a low-resistance path is created between two points in an electric circuit that are normally at different potentials, often bypassing the intended load.

According to Ohm’s Law, the current (I) flowing through a circuit is directly proportional to the voltage (V) across it and inversely proportional to the resistance (R): I = V/R. During a short-circuit, the resistance of the path drops significantly, often close to zero. Assuming the voltage source remains relatively constant, a drastic decrease in resistance leads to a massive increase in the current flowing through the circuit.

This heavy increase in current during a short-circuit can cause overheating of wires and components due to the power dissipated (P = I²R), potentially leading to damage, fire, or explosion. Safety devices like fuses and circuit breakers are designed to detect this excessive current and interrupt the circuit, preventing damage.

8. What is the correct sequence of resistivity of silver, nichrome and gl

What is the correct sequence of resistivity of silver, nichrome and glass at room temperature ?

[amp_mcq option1=”Silver < Nichrome < Glass" option2="Glass < Nichrome < Silver" option3="Silver < Glass < Nichrome" option4="Nichrome < Silver < Glass" correct="option1"]

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

Resistivity is an intrinsic property of a material that quantifies how strongly it opposes the flow of electric current. Materials are classified as conductors, semiconductors, or insulators based on their resistivity values.

Good electrical conductors have very low resistivity. Metals like silver are excellent conductors. Alloys like nichrome are generally poorer conductors than pure metals and have higher resistivity. Insulators have very high resistivity, effectively preventing current flow. Glass is a good insulator. Therefore, the correct order of resistivity from lowest to highest is Silver (conductor) < Nichrome (alloy) < Glass (insulator).

At room temperature, the resistivity values are approximately: Silver ~ 1.59 × 10⁻⁸ Ω·m, Nichrome ~ 1.1 × 10⁻⁶ Ω·m, Glass ~ 10¹⁰ to 10¹⁴ Ω·m. This confirms the order: Silver < Nichrome < Glass. Nichrome's relatively high resistivity makes it suitable for heating elements in appliances like toasters and heaters.

9. If the magnification produced by a lens is +2, then the image is :

If the magnification produced by a lens is +2, then the image is :

erect, virtual and smaller than the object.

inverted, real and smaller than the object.

erect, virtual and larger than the object.

inverted, real and larger than the object.

This question was previously asked in

UPSC CDS-1 – 2022

Download PDF Attempt Online

The magnification produced by a lens is given by the ratio of the image height to the object height (m = h’/h). The sign of the magnification provides information about the nature and orientation of the image.

A positive magnification (+m) indicates that the image is erect (upright) relative to the object. A negative magnification (-m) indicates that the image is inverted. The magnitude of the magnification (|m|) indicates the size of the image relative to the object: |m| > 1 means the image is larger, |m| = 1 means it’s the same size, and |m| < 1 means it's smaller. A magnification of +2 means the image is erect (due to the + sign) and is twice the size of the object (|2| > 1). For a single lens, an erect image is always a virtual image.

Real images formed by a single lens are always inverted, and virtual images are always erect. Therefore, a positive magnification (+2) implies an erect and virtual image that is magnified (larger than the object). This type of image is typically formed by a converging (convex) lens when the object is placed within its focal length.

10. The size of particles being studied in ‘nano-technology’ is about

The size of particles being studied in ‘nano-technology’ is about

1 Å – 10 nm

1 – 100 nm

1 – 50 µ

1 mm – 10 mm

This question was previously asked in

UPSC CDS-1 – 2021

Download PDF Attempt Online

Nanotechnology is broadly defined as the understanding, manipulation, and control of matter at the nanoscale, typically ranging from approximately 1 to 100 nanometers (nm).

A nanometer (nm) is one billionth of a meter (10⁻⁹ m). The 1 to 100 nm range is considered the nanoscale because materials within this size range often exhibit unique physical, chemical, and biological properties that differ significantly from their bulk counterparts. This is due to quantum mechanical effects and a large surface area-to-volume ratio.

Different units of measurement relate to nanometers as follows: 1 Ångstrom (Å) = 0.1 nm, 1 micrometer (µm) = 1000 nm, 1 millimeter (mm) = 1,000,000 nm. Option A (1 Å – 10 nm) is a narrower range within the nanoscale. Options C and D represent the microscale and millimeter scale, respectively, which are much larger than the nanoscale.