UPSC NDA-1

21. An atom of carbon has 6 protons. Its mass number is 12. How many neutr

An atom of carbon has 6 protons. Its mass number is 12. How many neutrons are present in an atom of carbon?

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12
6
10
14
This question was previously asked in
UPSC NDA-1 – 2016
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The correct answer is B) 6.
The mass number (A) of an atom is the total number of protons and neutrons in the nucleus. The number of protons is equal to the atomic number (Z). Therefore, the number of neutrons (N) can be calculated using the formula: N = A – Z.
For the given carbon atom:
Number of protons (Z) = 6
Mass number (A) = 12
Number of neutrons (N) = Mass number (A) – Number of protons (Z) = 12 – 6 = 6.
Thus, there are 6 neutrons in an atom of carbon with mass number 12. This specific isotope is Carbon-12 (¹²C), the most common isotope of carbon.

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22. The S.I. unit of acceleration is

The S.I. unit of acceleration is

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ms⁻¹
ms⁻²
cms⁻²
kms⁻²
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The correct answer is B) ms⁻².
Acceleration is the rate of change of velocity with respect to time. The S.I. unit for velocity is meters per second (m/s or ms⁻¹) and the S.I. unit for time is seconds (s).
The unit of acceleration is derived by dividing the unit of velocity by the unit of time: (m/s) / s = m/s² = ms⁻². Options A, C, and D represent units of velocity (ms⁻¹), acceleration in CGS units (cms⁻²), and acceleration in a non-standard or larger unit (kms⁻²), respectively.

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23. During solar eclipse

During solar eclipse

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the earth comes in between the sun and the moon.
the moon comes in between the sun and the earth.
the moon comes exactly halfway between the earth and the sun.
the sun comes in between the earth and the moon.
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The correct answer is B) the moon comes in between the sun and the earth.
A solar eclipse occurs when the Moon passes directly between the Sun and Earth, casting a shadow on Earth and blocking the Sun’s light.
The alignment for a solar eclipse is always Sun – Moon – Earth. During a solar eclipse, the Moon covers the Sun either partially or completely (total solar eclipse) for observers on Earth within the shadow cone. This is in contrast to a lunar eclipse, where the Earth comes between the Sun and the Moon.

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24. Two bodies A and B are moving with equal velocities. The mass of B is

Two bodies A and B are moving with equal velocities. The mass of B is double that of A. In this context, which one of the following statements is correct?

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Momentum of B will be double that of A.
Momentum of A will be double that of B.
Momentum of B will be four times that of A.
Momenta of both A and B will be equal.
This question was previously asked in
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The correct answer is A) Momentum of B will be double that of A.
Momentum (p) of an object is defined as the product of its mass (m) and velocity (v): p = m * v. Given that both bodies A and B are moving with equal velocities (v_A = v_B = v) and the mass of B is double that of A (m_B = 2 * m_A).
Calculating the momentum for each body:
Momentum of A: p_A = m_A * v_A = m_A * v
Momentum of B: p_B = m_B * v_B = (2 * m_A) * v = 2 * (m_A * v)
Comparing p_B with p_A, we find that p_B = 2 * p_A. Therefore, the momentum of B will be double that of A.

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25. Structurally, the Meghalaya region is a part of

Structurally, the Meghalaya region is a part of

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Shiwalik Range
Deccan Plateau
Greater Himalaya
Aravalli Range
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The correct answer is B) Deccan Plateau.
Geologically, the Meghalaya region (also known as the Shillong Plateau) is considered an outlier or extension of the Indian Peninsular Plateau, which includes the Deccan Plateau. It is separated from the main block of the Peninsular Plateau by the Malda Fault (also known as the Garo-Rajmahal Gap).
Despite being part of the Peninsular Plateau system, the Meghalaya Plateau has undergone significant faulting and uplift, leading to its distinctive topography and high rainfall. It is not structurally related to the Himalayan ranges (Shiwalik or Greater Himalaya) or the Aravalli Range.

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26. In India, glacial terraces known as ‘Karewas’ are found in

In India, glacial terraces known as ‘Karewas’ are found in

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Sapt Kosi Valley
Jhelum Valley
Alakananda Valley
Teesta Valley
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The correct answer is B) Jhelum Valley.
Karewas are specific geological formations, essentially glacio-lacustrine deposits (sediments deposited in a lake formed by glacial activity), found primarily in the Kashmir Valley. The main river draining the Kashmir Valley is the Jhelum.
Karewas are flat-topped terraces known for their fertility and suitability for cultivating saffron, almonds, and other crops. They are composed of clays, silts, sands, lignite, and pebbles. These deposits provide valuable insights into the Quaternary geological and palaeoclimatic history of the region.

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27. Which of the following substances are harmful for health if present in

Which of the following substances are harmful for health if present in food items?

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  • 1. Pesticide residues
  • 2. Lead
  • 3. Metanil yellow
  • 4. Mercury

Select the correct answer using the code given below:

1 and 2 only
1, 2 and 4 only
3 and 4 only
1, 2, 3 and 4
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The correct answer is D) 1, 2, 3 and 4.
All the substances listed – Pesticide residues, Lead, Metanil yellow, and Mercury – are considered harmful to human health if present in food items.
– **Pesticide residues:** Chemicals used to control pests can remain on or in food crops and pose health risks when consumed.
– **Lead:** A heavy metal that is highly toxic and can accumulate in the body, causing severe health problems, especially in children. It can enter food through contaminated water, soil, or processing equipment.
– **Metanil yellow:** A non-permitted food colour often used illegally to colour food items like sweets and spices. It is a harmful chemical that can cause neurological damage and other health issues.
– **Mercury:** Another toxic heavy metal. Organic mercury compounds like methylmercury can build up in fish and seafood, posing risks to humans who consume them. Inorganic mercury can also contaminate food sources.
All these substances are regulated by food safety authorities, with maximum permissible limits set for their presence in food.

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28. Mass of a particular amount of substance 1. is the amount of matter

Mass of a particular amount of substance

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  • 1. is the amount of matter present in it.
  • 2. does not vary from place to place.
  • 3. changes with change in gravitational force.

Select the correct answer using the code given below :

1, 2 and 3
1 and 2 only
2 and 3 only
1 only
This question was previously asked in
UPSC NDA-1 – 2016
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Let’s analyze each statement about the mass of a particular amount of substance:
1. is the amount of matter present in it: This is the fundamental definition of mass. Mass is a measure of the inertia of an object, which is directly related to the quantity of matter it contains. This statement is true.
2. does not vary from place to place: Mass is an intrinsic property of an object. Unlike weight, which depends on the gravitational acceleration, mass remains constant regardless of the location (e.g., on Earth, the Moon, or in space). This statement is true.
3. changes with change in gravitational force: This statement is false. Weight (W) changes with gravitational force (g) according to the formula W = m * g. As gravity changes, weight changes, but mass (m) itself remains constant. For example, an object weighs less on the Moon than on Earth because the Moon’s gravity is weaker, but its mass is the same in both locations.
Mass is a measure of the amount of matter and is constant for a given object, independent of gravity. Weight is the force of gravity acting on an object’s mass and varies with gravitational acceleration.
Mass is measured in units like kilograms (kg) or grams (g). Weight is a force and is measured in units like Newtons (N) or pounds (lb).

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29. Soap is sodium or potassium salt of

Soap is sodium or potassium salt of

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Stearic acid
Oleic acid
Palmitic acid
All of the above
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Soaps are traditionally made by the saponification of fats or oils with a strong alkali, such as sodium hydroxide (for hard soap) or potassium hydroxide (for liquid soap). Fats and oils are triglycerides, which are esters formed from glycerol and fatty acids. Saponification breaks down the triglyceride into glycerol and the sodium or potassium salts of the fatty acids.
Common fatty acids found in fats and oils used for soap making include saturated fatty acids like stearic acid (C₁₇H₃₅COOH) and palmitic acid (C₁₅H₃₁COOH), and unsaturated fatty acids like oleic acid (C₁₇H₃₃COOH). Therefore, soap is the sodium or potassium salt of long-chain fatty acids like stearic acid, oleic acid, and palmitic acid.
Soaps are salts of fatty acids. Saponification involves reacting fats/oils (triglycerides of fatty acids) with a strong base (NaOH or KOH) to produce soap (fatty acid salt) and glycerol.
The general formula for a soap molecule is R-COONa (sodium soap) or R-COOK (potassium soap), where R is a long hydrocarbon chain derived from a fatty acid. The long hydrocarbon chain is nonpolar and hydrophobic (water-repelling), while the carboxylate head (-COO⁻Na⁺ or -COO⁻K⁺) is polar and hydrophilic (water-attracting). This dual nature allows soap to emulsify grease and dirt in water.

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30. A body has a free fall from a height of 20 m. After falling through a

A body has a free fall from a height of 20 m. After falling through a distance of 5 m, the body would

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lose one-fourth of its total energy
lose one-fourth of its potential energy
gain one-fourth of its potential energy
gain three-fourth of its total energy
This question was previously asked in
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Let the total height be H = 20 m. The initial height is H = 20 m. After falling through a distance of 5 m, the body is at a height of h = 20 m – 5 m = 15 m from the ground.
We use the principle of conservation of mechanical energy, assuming no air resistance. Total Mechanical Energy (TE) = Potential Energy (PE) + Kinetic Energy (KE).
Initial state (at 20 m height):
Initial PE = mgH = mg(20).
Initial KE = 0 (free fall starts from rest).
Initial TE = mg(20) + 0 = 20mg.

After falling 5 m (at 15 m height):
Potential Energy at 15m = PE’ = mgh = mg(15).
The loss in potential energy is Initial PE – PE’ = 20mg – 15mg = 5mg.
The fraction of the *initial* potential energy lost is (Loss in PE) / (Initial PE) = (5mg) / (20mg) = 1/4.

By conservation of energy, the energy lost from potential energy is gained as kinetic energy.
KE gained = Loss in PE = 5mg.
Kinetic Energy at 15m = KE’ = 5mg.
Total Energy at 15m = PE’ + KE’ = 15mg + 5mg = 20mg. The total energy remains constant.

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Let’s evaluate the options:
A) lose one-fourth of its total energy: Incorrect, total energy is conserved.
B) lose one-fourth of its potential energy: The initial potential energy was 20mg. The loss is 5mg, which is indeed one-fourth (1/4) of the initial potential energy. Correct.
C) gain one-fourth of its potential energy: Incorrect, potential energy decreases as the body falls.
D) gain three-fourth of its total energy: Incorrect, total energy is conserved.

Note: If the question meant “lose one-fourth of its *remaining* potential energy”, that would be different, but the phrasing “lose one-fourth of its total potential energy” usually refers to the initial maximum potential energy.

In free fall (assuming no air resistance), mechanical energy is conserved. As potential energy decreases, kinetic energy increases by an equal amount. Potential energy is proportional to height.
The loss of potential energy is equal to the gain in kinetic energy. After falling 5m from 20m, the body is at 15m. The initial PE was proportional to 20m, the PE at 15m is proportional to 15m. The drop in PE is proportional to 5m. 5/20 = 1/4, meaning 1/4 of the *initial* PE is lost, and 1/4 of the initial PE is converted into KE.

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