Assertions and Reasons MCQ Quiz - Objective Question with Answer for Assertions and Reasons - Download Free PDF

The most appropriate answer is  Both (A) and (R) are correct and (R) is the correct explanation of (A).

Important Points 

Assertion (A): Large dams on rivers tend to reduce the fertility of land areas in the river floodplain.

• This assertion is correct.
• Large dams built on rivers can alter the natural flow of the river and reduce the deposition of silt on the river floodplain.
• Silt is rich in nutrients and helps to enrich the soil in the flood plain, which is important for agriculture and other forms of land use.
• When dams are built, the silt is trapped behind the dam, reducing the amount that reaches the flood plain downstream.
• This can result in a reduction in soil fertility, which can negatively impact agriculture and other land use practices in the area.

Reason (R): Dams reduce the deposition of silt over land areas in the river floodplain.

• This reason is also correct and provides a logical explanation for the assertion.
• Dams trap sediment and silt, preventing it from being deposited downstream.
• As a result, the amount of silt that reaches the floodplain is reduced, which can negatively impact soil fertility.

Therefore, Both (A) and (R) are correct and (R) is the correct explanation of (A) is the most appropriate answer.

Additional Information  Environmental impact of Dams

Habitat fragmentation:

• Unless specifically engineered to allow fish to pass through them, dams present a barrier to fish that need to migrate to spawn and reproduce downstream and upstream along a river. 

Flooding and the destruction of surrounding habitat:

• Dammed rivers create a reservoir upstream from the dam, which spills out into the surrounding environments and floods ecosystems and habitats that once existed there. Such flooding can kill or
• displace many different organisms, including plants, wildlife, and humans.

Greenhouse gases:

• The flooding of the surrounding habitat around dams kills trees and other plant life that
• then decomposes and releases large amounts of carbon into the atmosphere. 

Sediment builds up behind the dam:

• Because a dammed river no longer flows freely, the sediment that would have otherwise been deposited naturally downstream begins to build up behind the dam, forming new riverbanks, river deltas, alluvial fans, braided rivers, oxbow lakes, levees, and coastal shores.
• These changes in sedimentation can lead to dramatic alterations in plant life and animal life and how they are distributed.

​Downstream sediment erosion:

• Due to the restrictions in the sediment flow above a dam, the lack of sediment that would have once flowed downstream ultimately leads to a deficiency in sediment load, and therefore, leads to an increase in downstream erosion.
• This lack of sediment load causes the riverbed to deepen and narrow over time, a compromised water table, the homogenization of the river’s flow, reduced wildlife support, and a reduction in sediment that reaches coasts and deltas.

Negative impacts on local fish populations:

• Typically, local fish species will not be adapted to the new environment that is present after a dam is built and do not survive, leading to the extirpation of local populations. 

Production of methyl-mercury:

• The stagnant water in reservoirs creates a situation where the decomposition of organic matter from decaying plants can transform inorganic mercury into methylmercury.
• Unfortunately, methyl-mercury tends to bio-accumulate and cause toxic effects in humans and wildlife that eat the fish in reservoirs

Assertion (A):

Salt is added to cook food at higher altitudes.

→ It is true because at higher altitudes, pressure is decreased and the water is boiled below 100° Celsius. Thus, adding salt to the water to cook food increases the boiling point of water.

Reason (R):

Temperature lower at higher altitudes.

→ It is true because as the altitude increases, the temperature gets lower.

Thus, both (A) and (R) are true but (R) is not the correct explanation (A).

Hence, the correct answer is "Both A and R are true but R is not the correct explanation of A".

The logic followed here is: 

Assertion (A) : Plaster of Paris is used for setting fractured bones by doctors.

→ True, Plaster of Paris is mixed with water and used around the fractured limb, it sets into a hard mass and keeps the bone joints in a fixed position, and is used for setting fractured bones.

Reason (R) : If Plaster of Paris is mixed with water and used around the fractured limb, it sets into a hard mass.

→  The Reason is the correct explanation of A, as Plaster of Paris is used for setting fractured bones.

Hence, the correct answer is "Both A and R are true and R is the correct explanation of A".

The greenhouse effect is a process in which gases in the earth's atmosphere capture the Sun's heat. 

Key PointsAssertion (A): Chlorofluorocarbons (CFCs) are potent greenhouse gases.

• This is true. Chlorofluorocarbons, or CFCs, are a type of compound that was widely used during the 20th century in applications like air conditioning, refrigeration, and aerosol propellants.
• The issue with these substances is that they are very stable and do not break down in the lower atmosphere after they are released.
• Consequently, they slowly ascend to higher altitudes, where they absorb and emit infrared radiation, contributing to the greenhouse effect.

So, Assertion (A) is correct. 

Reasons (R): CFCs have the ability to catalytically destroy ozone in stratosphere.

• The ozone layer is situated in the stratosphere of Earth's poles. 
• The main gases for ozone depletion are halocarbon refrigerants, solvents, propellants, and chlorofluorocarbons (CFCs), HCFCs, halons. 
• CFCs ascend into the stratosphere are oxidized by potent UV light, and then interact with ozone molecules that affect the Ozone layer. 

Thus, Reasons (R) is correct. 

Therefore, both (A) and (R) are correct but (R) is NOT the correct explanation of (A)

Explanation:- Light is an electromagnetic wave and hence it has a speed which is much higher than the speed of sound. So during lightning, the light reaches earlier than the sound. So the assertion is incorrect but the reason is correct.

The flash of lightning during a thunderstorm is a light ray which is an electromagnetic wave. The speed of light in vaccum is given by 3 x 10⁸m/s which is much more than the speed of sound.

So when lightning strikes then the flash of light reaches us much faster than the sound does.

Hence, the correct answer is A is false but R is true.

The doctrine of Lapse was adopted as an annexation policy with respect to the expansionist tendencies of the British East India Company.

And according to the policy, if a ruler was incompetent or left without a male heir to the throne, the state was bound to lose its princely status.

So, the assertion is correct.

Also, this policy was widely implemented by Lord Dalhousie, who was the Governor-General of the East India Company in India between 1848 and 1856 but actually the policy was drafted in 1847.

So, the stated reason is correct but does not explain the assertion.

Option(1) is correct.

Assertion: Moon cannot be used as a satellite for communication - True as Moon is very far away from Earth (the orbital time period is approximately 27.3 days), also it does not have an equatorial orbit nor have a polar orbit.

Reason (R): Moon does not move in the equatorial plane of the earth - True and that's why it cannot be used as a satellite for communication.

Hence, the correct answer is Option(1) i.e., Both A and R are true and R is the correct explanation of A.

Assertion (A):

Methane gas released by some industries leads to global warming. → True

Reason (R):

Methane is a heavy gas and it settles in the lower regions of the atmosphere. → False

Methane is a strong greenhouse gas with a global warming potential 84 times higher than Carbon dioxide. 

Hence, A is true but R is false.

Assertion (A): Ventilators are provided near the roof. → True

It is true that ventilators are provided near the roof.

Reason (R): Conduction takes place better near the roof. → False

Conduction is the transfer of energy through a medium, from higher energy level to lower energy level.

Hence, A is true but R is false.

The assertion that all cockroaches are brown is not correct as some species of cockroaches are not brown but, the given reason is correct.

Hence, the given assertion is false but the reason is true.

Since the disease is caused by the Influenza virus, the government needs to control the spread of the virus to stop the spread of the disease which is stated in conclusion II. Hence conclusion II follows. 

There is no information provided in the statement to suggest that the disease is fatal. Therefore, conclusion I cannot be drawn from the given statements and 2 is the right option. 

Forest has been gradually decreased because of increased population. Human cuts the forest and make houses. Many more thing are there to cut trees. Illegal cutting of trees one of the main concerns. So here reason is the best suitable for the given assertion.

The assertion is correct because it is true that rocket science is also built upon the basic concepts of Newton with a complex calculation and numerous possibilities.
Hence, the assertion is true.

But the reason is not correct as it says that anyone can make a rocket on his own which is logically inconsistent.
Therefore, the reason is false.

Hence, A is true, but R is false

Vehicles emit carbon dioxide which is a greenhouse gas.

Therefore, Reason (R) is true.

Therefore, increase in average cars on road means increase in carbon emissions.

Therefore, Assertion(A) is true.

Hence, (A) is true and (R) is true and (R) is the correct explanation of (A).

It is true that black money is a big problem in India and that the prices of goods are increasing rapidly in the country. But the reason is not the complete explanation behind the assertion.