UPSC CDS-2

1. Desalination of seawater is done by using reverse osmosis. The pressur

Desalination of seawater is done by using reverse osmosis. The pressure applied to the solution is

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larger than osmotic pressure
smaller than osmotic pressure
equal to osmotic pressure
equal to atmospheric pressure
This question was previously asked in
UPSC CDS-2 – 2017
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The correct answer is larger than osmotic pressure.
Osmosis is the spontaneous movement of solvent molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. Osmotic pressure is the pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution by osmosis, often used to express the concentration of the solution. Reverse osmosis is a process where a solvent is forced through a semipermeable membrane from a region of high solute concentration to a region of low solute concentration by applying a pressure greater than the osmotic pressure. This is the principle used in desalination to separate pure water from seawater.
In desalination using reverse osmosis, pressure is applied to the seawater (higher solute concentration) side of the membrane. This pressure overcomes the natural osmotic pressure and forces water molecules (solvent) through the membrane, leaving the salts behind. The membrane allows the passage of water molecules but not the dissolved salts.

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2. The foul smell of urine of a healthy man having healthy food, when spi

The foul smell of urine of a healthy man having healthy food, when spilled on floor, is mainly due to the bacterial decomposition of

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urea into sulphur dioxide
sugar into carbon dioxide
lipids into methane
urea into ammonia
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UPSC CDS-2 – 2017
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When urine containing urea is exposed to air, bacteria (such as those commonly found in soil or on surfaces) break down the urea through a process called hydrolysis, producing ammonia. Ammonia is a volatile gas with a strong, pungent odor that causes the foul smell.
The enzymatic decomposition of urea by bacteria yields ammonia and carbon dioxide.
Fresh urine from a healthy individual is usually sterile and has little odor. The characteristic strong smell develops upon standing or spilling, due to the bacterial breakdown of urea. This is why ammonia is often used in cleaning products, although its smell is undesirable in other contexts.

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3. Consider the following statements: 1. The chain reaction process is

Consider the following statements:

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  • 1. The chain reaction process is used in nuclear bombs to release a vast amount of energy, but in nuclear reactors, there is no chain reaction.
  • 2. In a nuclear reactor, the reaction is controlled, while in nuclear bombs, the reaction is uncontrolled.
  • 3. In a nuclear reactor, all operating reactors are ‘critical’, while there is no question of ‘criticality’ in case of a nuclear bomb.
  • 4. Nuclear reactors do not use moderators, while nuclear bombs use them.

Which of the above statements about operational principles of a nuclear reactor and a nuclear bomb is/are correct?

1 and 3
2 and 3
4 only
1 and 4
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UPSC CDS-2 – 2017
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Statement 2 is correct: Nuclear reactors operate under controlled chain reactions, while nuclear bombs involve uncontrolled chain reactions. Statement 3 is also considered correct in this context, highlighting the difference in operation: reactors maintain a controlled ‘critical’ state, while bombs rapidly achieve an uncontrolled ‘supercritical’ state, distinct from sustained critical operation.
The fundamental difference is control: a reactor controls the neutron population to sustain a steady chain reaction, while a bomb allows the neutron population to grow exponentially and uncontrollably.
Statement 1 is incorrect; both use chain reactions. Statement 4 is incorrect; nuclear reactors *do* use moderators (like water, heavy water, or graphite) to slow down neutrons, which is necessary for fission in materials like U-235, whereas nuclear bombs typically use fast neutrons and do not use moderators. Statement 3 is slightly awkwardly phrased, as criticality is essential to both, but the *way* criticality is achieved and maintained (controlled vs. uncontrolled, sustained vs. rapid) is different. Given the options, Statement 3 is intended to represent this difference in operational state relative to criticality.

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4. A person throws an object on a horizontal frictionless plane surface.

A person throws an object on a horizontal frictionless plane surface. It is noticed that there are two forces acting on this object—(i) gravitational pull and (ii) normal reaction of the surface. According to the third law of motion, the net resultant force is zero. Which one of the following can be said for the motion of the object?

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The object will move with acceleration.
The object will move with deceleration.
The object will move with constant speed, but varying direction.
The object will move with constant velocity.
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On a horizontal frictionless plane, the vertical forces (gravitational pull and normal reaction) are equal in magnitude and opposite in direction, resulting in zero net force in the vertical direction. If the object is thrown, it has an initial horizontal velocity. Since the plane is frictionless, there is no horizontal force (ignoring air resistance).
According to Newton’s first law of motion, an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force. With zero net force acting on the object in both vertical and horizontal directions, its velocity (magnitude and direction) remains constant.
The third law of motion states that for every action, there is an equal and opposite reaction. While it ensures that forces exist in pairs (e.g., Earth pulls the object down, object pulls Earth up; surface pushes object up, object pushes surface down), it doesn’t imply the *net resultant force on the object itself* is zero unless the forces acting *on that object* happen to be balanced. In this scenario, the forces *on the object* (gravity and normal reaction) are balanced vertically, and there are no horizontal forces, resulting in zero net force on the object, leading to constant velocity.

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5. Ultrasonic waves are produced by making use of

Ultrasonic waves are produced by making use of

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ferromagnetic material
ferrimagnetic material
piezoelectric material
pyroelectric material
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Ultrasonic waves are commonly produced by utilizing the piezoelectric effect, typically in materials like quartz crystals or certain ceramics.
Piezoelectric materials convert electrical energy into mechanical vibrations and vice versa. By applying a high-frequency alternating voltage across a piezoelectric crystal, it vibrates at that frequency, generating ultrasonic waves.
The piezoelectric effect is reversible. Piezoelectric materials are used in ultrasonic transducers for various applications, including medical imaging (ultrasound scans), sonar, industrial testing (non-destructive testing), and cleaning (ultrasonic cleaners).

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6. Joule-Thomson process is extremely useful and economical for attaining

Joule-Thomson process is extremely useful and economical for attaining low temperature. The process can be categorized as

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isobaric process
isoenthalpic process
adiabatic process
isochoric process
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The Joule-Thomson process (also known as the Joule-Kelvin effect) is an isoenthalpic process, meaning that the enthalpy of the gas or liquid remains constant during the expansion through a valve or porous plug.
In the Joule-Thomson process, a temperature change occurs when a real gas or liquid expands or is compressed adiabatically while flowing through a valve or throttling device. The process is performed at constant enthalpy.
For most gases (except hydrogen and helium at room temperature), the Joule-Thomson effect causes cooling upon expansion from high to low pressure, provided the initial temperature is below the gas’s inversion temperature. This effect is crucial in refrigeration, air conditioning, and the liquefaction of gases.

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7. ‘Xeriscaping’ is a concept related to

‘Xeriscaping’ is a concept related to

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landscaping related to save water
landscaping related to save soil erosion
weathering of rock surface
All of the above
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UPSC CDS-2 – 2017
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Xeriscaping is a type of landscaping that is designed to reduce or eliminate the need for irrigation, thus conserving water.
The term ‘xeri-‘ comes from the Greek word ‘xeros’, meaning dry. Xeriscaping utilizes drought-tolerant plants, efficient irrigation methods, and careful planning to minimize water usage in landscapes.
The principles of xeriscaping include proper design, soil improvement, efficient irrigation (e.g., drip irrigation), appropriate plant selection, mulching, and proper maintenance. While water conservation is the primary goal, it can also contribute to reducing maintenance costs and sometimes soil erosion.

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8. Which of the following radioactive substances enters/enter the human b

Which of the following radioactive substances enters/enter the human body through food chain and causes/cause many physiological disorders?

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Strontium-90
Iodine-131
Cesium-137
All of the above
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UPSC CDS-2 – 2017
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Strontium-90, Iodine-131, and Cesium-137 are all radioactive isotopes that can enter the human body through contaminated food and water sources, becoming part of the food chain, and causing various physiological disorders.
These radioactive isotopes can accumulate in specific organs or tissues due to their chemical similarity to essential elements (Sr-90 to Calcium, I-131 to Iodine, Cs-137 to Potassium), leading to cellular damage and increased cancer risk.
These isotopes are common byproducts of nuclear fission, released during nuclear accidents (like Chernobyl or Fukushima) or nuclear weapons testing. Their presence in the environment poses long-term health risks through contamination of soil, water, plants, and animals, ultimately affecting humans via the food chain.

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9. An emulsion consists of

An emulsion consists of

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one liquid and one solid
one liquid and one gas
two liquids
two solids
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UPSC CDS-2 – 2017
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An emulsion is a mixture of two liquids that are normally immiscible (unmixable or unblendable).
In an emulsion, one liquid is dispersed in the other in the form of tiny droplets.
Examples of emulsions include milk (fat dispersed in water) and vinaigrette (oil dispersed in vinegar). Emulsions are often stabilized by adding an emulsifying agent, which helps keep the two liquids dispersed and prevents separation.

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10. One carbon credit is accepted as equivalent to

One carbon credit is accepted as equivalent to

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100 kg of carbon
100 kg of carbon dioxide
1000 kg of carbon
1000 kg of carbon dioxide
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UPSC CDS-2 – 2017
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One carbon credit is generally accepted as equivalent to 1000 kg (or 1 metric tonne) of carbon dioxide (CO2) equivalent.
Carbon credits represent a measurable amount of greenhouse gas emissions reduced, avoided, or sequestered, standardized to 1 tonne of CO2 equivalent.
Carbon credits are a key component of carbon trading schemes, designed to reduce greenhouse gas emissions. They allow entities that reduce emissions below their cap to sell credits to those who exceed their cap, creating a market incentive for emission reduction. While often expressed in CO2 equivalent, this includes other greenhouse gases weighted by their global warming potential.

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