UPSC CISF-AC-EXE

21. Gases can be liquefied by

Gases can be liquefied by

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reducing pressure and temperature.
applying pressure and reducing temperature.
reducing pressure and raising temperature.
applying pressure and raising temperature.
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Gases can be liquefied by increasing the intermolecular forces or reducing the kinetic energy of the gas particles so that they can come closer together and form a liquid state. Applying pressure forces the particles closer, increasing intermolecular interactions. Reducing temperature decreases the kinetic energy of the particles, making it easier for them to form liquid bonds. Liquefaction occurs when the temperature is at or below the critical temperature and sufficient pressure is applied. The most effective way is typically applying pressure and reducing temperature.
Liquefaction of gases requires increasing pressure and/or decreasing temperature to bring molecules closer and reduce their kinetic energy.
For every gas, there is a critical temperature above which it cannot be liquefied by pressure alone. Below the critical temperature, increasing pressure can cause liquefaction. Reducing the temperature makes liquefaction easier at lower pressures. Therefore, applying pressure and reducing temperature together is the standard method for liquefying gases.

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22. In an atomic gas, the motion of particles (atoms) is governed by the c

In an atomic gas, the motion of particles (atoms) is governed by the collisions. If the gas is ionized, then the motion of created particles may be mainly governed by

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gravitational force.
collisions.
scattering of particles.
electromagnetic force between the particles.
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In an atomic gas, the atoms are electrically neutral, and their motion is primarily governed by collisions between them. When the gas is ionized, atoms lose or gain electrons, becoming charged particles (ions and free electrons). These charged particles exert strong electrostatic (electromagnetic) forces on each other over relatively long distances compared to the short-range forces involved in neutral collisions. Therefore, the motion of particles in an ionized gas (plasma) is mainly governed by the long-range electromagnetic forces between these charged particles, rather than just collisions.
In a neutral atomic gas, particle motion is dominated by collisions. In an ionized gas (plasma) containing charged particles, the motion is dominated by long-range electromagnetic forces between these charges.
An ionized gas is also known as plasma, which is often considered the fourth state of matter. The collective behavior of charged particles under the influence of electromagnetic fields is a key characteristic of plasma physics. While collisions still occur in plasma, their influence on overall motion is often less dominant than the electromagnetic forces, especially in hot, tenuous plasmas.

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23. The transfer of thermal energy carries which of the following

The transfer of thermal energy carries which of the following phenomena?

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Conduction and convection only
Only conduction
Conduction, convection and radiation
Only radiation
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Thermal energy, or heat, can be transferred from one place to another through three fundamental mechanisms: conduction, convection, and radiation. Conduction is the transfer of heat through direct contact of particles, primarily in solids. Convection is the transfer of heat through the movement of fluids (liquids or gases). Radiation is the transfer of heat through electromagnetic waves, which does not require a medium and can occur through a vacuum.
The three main modes of thermal energy transfer are conduction, convection, and radiation.
Examples: Conduction transfers heat through a metal rod when one end is heated. Convection transfers heat in boiling water or rising hot air. Radiation transfers heat from the sun to the Earth, or from a fire to your hands. All three phenomena contribute to the transfer of thermal energy in different situations.

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24. An electric refrigerator rated 400 W operates 10 hours/day. What is th

An electric refrigerator rated 400 W operates 10 hours/day. What is the cost of the energy to operate it for 30 days at ₹ 3.00 per kWh?

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₹ 360
₹ 3,600
₹ 36
₹ 400
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The power rating of the refrigerator is 400 W, which is equal to 0.4 kW (since 1 kW = 1000 W). The refrigerator operates for 10 hours per day. Over 30 days, the total operation time is 10 hours/day * 30 days = 300 hours. The total energy consumed is the power multiplied by the time: Energy (kWh) = Power (kW) * Time (hours) = 0.4 kW * 300 hours = 120 kWh. The cost of energy is ₹ 3.00 per kWh. Total cost = Energy consumed * Cost per kWh = 120 kWh * ₹ 3.00/kWh = ₹ 360.
Energy consumed is calculated as Power (in kW) multiplied by Time (in hours). The total cost is the energy consumed multiplied by the rate per unit of energy (kWh).
The unit of energy used for billing is typically the kilowatt-hour (kWh), often called a ‘unit’ of electricity. Power in watts needs to be converted to kilowatts before calculating energy in kWh if time is in hours.

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25. An object is kept at infinity from the position of a concave (spherica

An object is kept at infinity from the position of a concave (spherical) mirror. Which one is *not* true about the image of the object?

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Position of image is at the focus of the mirror
Size of image is the same as that of the object
Image is real
Image is inverted
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When an object is placed at infinity from a concave spherical mirror, the light rays from the object are considered to be parallel to the principal axis. After reflection from the concave mirror, these parallel rays converge at the principal focus (F) of the mirror. The image formed at the focus is real, inverted (relative to the infinitely distant object), and highly diminished (essentially a point image).
For an object at infinity from a concave mirror, the image is formed at the focus, is real, inverted, and highly diminished (point-sized).
Option A states the position of the image is at the focus, which is true. Option C states the image is real, which is true for converging rays formed on the same side as the object. Option D states the image is inverted, which is true for real images formed by a concave mirror (even though a point image doesn’t visually appear inverted). Option B states the size of the image is the same as that of the object, which is false; the image is highly diminished. Therefore, the statement that is *not* true is B.

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26. Tyndall effect appears due to which one of the following properties of

Tyndall effect appears due to which one of the following properties of light?

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Reflection of light
Diffraction of light
Polarization of light
Scattering of light
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The Tyndall effect is the phenomenon where the path of a beam of light becomes visible as it passes through a colloidal dispersion or a fine suspension. This effect occurs because the larger particles in the colloid or suspension scatter the light in all directions when it strikes them.
Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension.
Reflection occurs when light bounces off a surface. Diffraction is the bending of light waves as they pass around the edge of an obstacle or through a narrow slit. Polarization is the restriction of the vibration of light waves to a single plane. Scattering is the process by which light is deflected in various directions as it interacts with a medium or particles within it, which is the principle behind the Tyndall effect.

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27. Tigers have a shorter small intestine compared to cows. The length of

Tigers have a shorter small intestine compared to cows. The length of the small intestine differs in various animals depending on the

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availability of water in their habitat.
size of their mouth cavity.
kind of habitats where they live.
kind of food they eat.
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Tigers are carnivores and cows are herbivores. The length of the small intestine in animals is primarily adapted to the type of food they eat. Carnivores eat meat, which is relatively easy to digest and absorb, thus requiring a shorter digestive tract. Herbivores eat plant material, which is rich in cellulose and requires a longer, more complex digestive process, often involving fermentation by symbiotic microorganisms. A longer small intestine provides more surface area and time for the digestion and absorption of nutrients from plant matter.
The digestive system, including the length of the small intestine, is adapted to the diet of the animal. Herbivores have longer intestines than carnivores due to the difficulty in digesting plant cellulose.
The digestion of cellulose in herbivores often occurs in specialized chambers (like the rumen in cows) or in the hindgut, requiring a slower passage rate and a larger surface area for absorption, which is facilitated by a longer small intestine and overall digestive tract.

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28. Which one of the following nutrients is *not* available in

Which one of the following nutrients is *not* available in fertilizers?

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Iron
Nitrogen
Phosphorus
Potassium
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The question asks which nutrient is *not* available in fertilizers among the given options. All listed options (Iron, Nitrogen, Phosphorus, Potassium) are essential plant nutrients and are available in various types of fertilizers. Nitrogen, Phosphorus, and Potassium are primary macronutrients commonly found in NPK fertilizers, which form the bulk of the fertilizer industry. Iron is a micronutrient, required in smaller quantities, but is also available in specific micronutrient fertilizers (e.g., iron chelates) and is often included in complete fertilizer blends.
While all options are plant nutrients and can be found in fertilizers, Nitrogen, Phosphorus, and Potassium are the primary macronutrients (needed in large quantities) and form the basis of most common fertilizers. Iron is a micronutrient (needed in smaller quantities).
The phrasing of the question is potentially misleading, as Iron is indeed available in fertilizers. However, in the context of multiple-choice questions where one option must be selected, and considering the prominence of N, P, and K as the main components of standard fertilizers compared to Iron which is a micronutrient supplement, Iron might be considered the intended answer if the question is implicitly distinguishing between macronutrients and micronutrients in the context of bulk fertilization, despite the poor wording. Given the options, Iron is the least likely to be a major component of a general fertilizer compared to N, P, and K.

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29. During photosynthesis, O₂ of the atmosphere is fixed with the help of

During photosynthesis, O₂ of the atmosphere is fixed with the help of H₂O and sunlight to synthesize carbohydrate and O₂ is evolved by the splitting of

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CO₂
H₂O
NO₃⁻
PO₄³⁻
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During photosynthesis, $O_2$ is evolved by the splitting of H₂O.
– Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment.
– The overall equation for photosynthesis is $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{Light Energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.
– The process occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle).
– The light-dependent reactions take place in the thylakoid membranes of chloroplasts. In this stage, light energy is absorbed by chlorophyll, leading to the splitting of water molecules ($H_2O$). This process is called photolysis.
– Photolysis of water ($2H_2O \rightarrow 4e^- + 4H^+ + O_2$) releases electrons (used in the electron transport chain to produce ATP and NADPH), protons ($H^+$), and oxygen gas ($O_2$) as a byproduct. This oxygen is released into the atmosphere.
– The light-independent reactions (Calvin cycle) take place in the stroma of chloroplasts and use the ATP and NADPH produced during the light reactions to fix carbon dioxide ($CO_2$) from the atmosphere and synthesize carbohydrates.
– The question contains a slight inaccuracy by stating “$O_2$ of the atmosphere is fixed with the help of $H_2O$ and sunlight…”. It should be “$CO_2$ of the atmosphere is fixed…”. However, the second part of the sentence correctly asks what $O_2$ is evolved from.
– Based on the mechanism of photosynthesis, the oxygen gas evolved comes directly from the splitting of water molecules during the light-dependent stage.
The origin of oxygen produced during photosynthesis was a significant scientific question. Experiments using isotopic tracers ($^{18}O$) demonstrated that the oxygen evolved comes from water and not from carbon dioxide.

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30. Which of the following organelle(s) in an animal cell would have DNA a

Which of the following organelle(s) in an animal cell would have DNA and RNA?

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Nucleus only
Nucleus and mitochondria only
Nucleus, mitochondria and ribosomes
Mitochondria only
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In an animal cell, the Nucleus and mitochondria only would have DNA and RNA.
– DNA (Deoxyribonucleic Acid) is the primary genetic material in most organisms. In eukaryotic cells, the majority of DNA is found in the nucleus (nuclear DNA), forming chromosomes.
– Eukaryotic cells also contain DNA in certain organelles: mitochondria (mitochondrial DNA or mtDNA) and, in plant cells and some other eukaryotes, chloroplasts (chloroplast DNA or cpDNA). Animal cells lack chloroplasts.
– RNA (Ribonucleic Acid) is involved in protein synthesis and other cellular processes. Various types of RNA (mRNA, tRNA, rRNA) are transcribed from DNA.
– In animal cells:
– Nucleus: Contains the main genome (DNA) and is where transcription occurs, producing various types of RNA. Thus, the nucleus has both DNA and RNA.
– Mitochondria: Contain their own circular DNA (mtDNA) and also have ribosomes (mitoribosomes) made of ribosomal RNA (mt-rRNA) and proteins, and produce their own mRNA and tRNA. Thus, mitochondria have both DNA and RNA.
– Ribosomes: Are complex molecular machines responsible for protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins. Ribosomes themselves do not contain DNA. They read mRNA to build proteins.
– Therefore, in an animal cell, the nucleus and mitochondria are the organelles that contain both DNA and RNA.
While RNA is widely present in the cytoplasm (as mRNA being translated, tRNA carrying amino acids, and ribosomes containing rRNA), the question asks about *organelles* that contain both DNA and RNA. Ribosomes are technically organelles (or macromolecular machines depending on definition), but they lack DNA. The nucleus and mitochondria fit the criteria.

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