CUET PG 2026 Environmental Sciences Question Paper with Solutions

Concept:

Earth’s atmosphere is divided into several layers based on temperature variation with altitude. These layers are:


Troposphere – The lowest layer where weather phenomena occur.
Stratosphere – The second layer that contains the ozone layer.
Mesosphere – The layer where meteors burn up.
Thermosphere – The upper layer where auroras occur and satellites orbit.


The ozone layer is a region rich in ozone (\(O_3\)) molecules located mainly in the stratosphere, approximately \(15\)–\(35\) km above the Earth's surface. It plays a crucial role in absorbing harmful ultraviolet (UV) radiation from the Sun.



Step 1: Identifying the atmospheric layer containing ozone.

The ozone layer is concentrated in the stratosphere, where ozone molecules absorb most of the Sun's harmful ultraviolet radiation.



Step 2: Eliminating other options.


Troposphere: Contains weather systems but not the ozone layer.
Mesosphere: Known for meteor burning, not ozone concentration.
Thermosphere: Very thin air, contains ionized gases but not the ozone layer.


Thus, the correct atmospheric layer containing the ozone layer is the Stratosphere. Quick Tip: Remember the order of atmospheric layers from Earth's surface upward: \textbf{Troposphere → Stratosphere → Mesosphere → Thermosphere}. The \textbf{ozone layer is located in the Stratosphere}.

Concept:

Bowen’s Reaction Series describes the order in which minerals crystallize from a cooling magma. As magma cools, minerals form at different temperatures depending on their chemical composition.

The series is divided into two main branches:


Discontinuous series: Olivine → Pyroxene → Amphibole → Biotite
Continuous series: Calcium-rich plagioclase → Sodium-rich plagioclase


Minerals at the top of the series crystallize at the highest temperatures. Minerals toward the bottom crystallize at lower temperatures.



Step 1: Understanding the highest temperature mineral.

At very high temperatures (about \(1200^\circ C\)), the first mineral to crystallize from a cooling silicate magma is Olivine. It is rich in magnesium and iron and forms early during magma cooling.



Step 2: Position of other minerals in the series.


Quartz: Crystallizes at the lowest temperatures.
Biotite: Forms later in the discontinuous branch.
Muscovite: Forms at relatively low temperatures.


Since Olivine crystallizes first at the highest temperature, it is the correct answer. Quick Tip: In Bowen’s Reaction Series, remember the order of the discontinuous branch: \textbf{Olivine → Pyroxene → Amphibole → Biotite}. The mineral that crystallizes first from magma is \textbf{Olivine}.

Concept:

Minamata disease is a severe neurological disorder caused by poisoning from methylmercury, an organic form of mercury. It occurs when humans consume fish or shellfish contaminated with mercury compounds released into water bodies.

The disease was first discovered in 1956 in Minamata Bay, Japan, where industrial wastewater from a chemical factory discharged mercury into the sea. This mercury accumulated in aquatic organisms and entered the human food chain through biomagnification.

Exposure to methylmercury damages the central nervous system, leading to serious health problems.



Step 1: Identifying the toxic chemical responsible.

The primary chemical responsible for Minamata disease is methylmercury, which is a highly toxic compound of mercury. It accumulates in fish and shellfish and enters the human body through consumption.



Step 2: Understanding the symptoms caused by mercury poisoning.

Some common symptoms of Minamata disease include:


Loss of coordination
Numbness in hands and feet
Muscle weakness
Vision and hearing impairment
In severe cases, paralysis and death


Since the disease is caused by mercury contamination, the correct answer is Mercury. Quick Tip: \textbf{Minamata disease} is caused by \textbf{methylmercury poisoning} due to consumption of contaminated seafood. Remember: \textbf{Minamata → Mercury pollution}.

Concept:

The energy of a photon is given by the Planck–Einstein relation:
\[ E = \frac{hc}{\lambda} \]

where:


\(E\) = Energy of the photon
\(h\) = Planck’s constant \(= 6.6 \times 10^{-34}\ Js\)
\(c\) = Speed of light \(= 3 \times 10^8\ m/s\)
\(\lambda\) = Wavelength of the photon


Before substituting, convert the wavelength from nanometers to meters:
\[ 500\ nm = 500 \times 10^{-9}\ m = 5 \times 10^{-7}\ m \]



Step 1: Substitute the values into the photon energy formula.
\[ E = \frac{(6.6 \times 10^{-34})(3 \times 10^8)}{5 \times 10^{-7}} \]



Step 2: Simplify the numerator.
\[ 6.6 \times 3 = 19.8 \]
\[ E = \frac{19.8 \times 10^{-26}}{5 \times 10^{-7}} \]



Step 3: Divide the coefficients and adjust powers of ten.
\[ E = 3.96 \times 10^{-19}\ J \]

Thus, the energy of the photon is:
\[ E = 3.96 \times 10^{-19}\ J \] Quick Tip: To quickly estimate photon energy, remember the formula \(E = \frac{hc}{\lambda}\). Shorter wavelengths correspond to \textbf{higher photon energy}.

Concept:

Ozone Depleting Substances (ODS) are chemicals that damage the ozone layer in the stratosphere. Examples include chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform. These substances release chlorine or bromine atoms in the atmosphere, which break down ozone molecules and reduce the protective ozone shield.

To address this global environmental problem, countries signed the Montreal Protocol in 1987. This international treaty aims to phase out the production and consumption of ozone-depleting substances worldwide.



Step 1: Identifying the treaty related to ozone protection.

The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted in 1987 and is considered one of the most successful environmental agreements. It established a timetable for reducing and eventually eliminating the use of ODS.



Step 2: Eliminating the other options.


Kyoto Protocol: Focuses on reducing greenhouse gas emissions to combat climate change.
Paris Agreement: A global treaty addressing climate change and limiting global warming.
Basel Convention: Regulates the transboundary movement and disposal of hazardous wastes.


Since the agreement that specifically targets the phase-out of ozone-depleting substances is the Montreal Protocol, it is the correct answer. Quick Tip: \textbf{Montreal Protocol (1987)} → Protects the ozone layer by phasing out \textbf{CFCs and other ODS}. Remember: \textbf{Montreal = Ozone protection}.

Concept:

Biological Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen required by microorganisms to decompose organic matter present in water. It is commonly used as an indicator of the level of organic pollution in aquatic ecosystems.

When organic wastes such as sewage, agricultural runoff, or industrial effluents enter water bodies, microorganisms break down these substances using dissolved oxygen.


High BOD → Large amount of organic matter present → Microorganisms consume more oxygen.
Low BOD → Less organic pollution → Water is relatively clean.


If too much oxygen is consumed during decomposition, aquatic organisms like fish and invertebrates may suffer due to oxygen depletion.



Step 1: Understanding what a high BOD value represents.

A high BOD value means microorganisms require a large amount of oxygen to break down the organic material present in the water.



Step 2: Implication for water quality.

Because oxygen is heavily consumed, less dissolved oxygen remains available for aquatic life. This condition leads to poor water quality and high organic pollution.

Therefore, a high BOD indicates polluted water with high organic matter content. Quick Tip: \textbf{BOD is directly proportional to water pollution.} Higher BOD → More organic waste → Lower dissolved oxygen → Poor water quality.

Concept:

The Mohs Scale of Hardness is a qualitative scale used to measure the resistance of a mineral to scratching. It was developed by the German mineralogist Friedrich Mohs in 1812. The scale ranges from 1 (softest) to 10 (hardest).

The standard Mohs hardness scale is:


1 – Talc
2 – Gypsum
3 – Calcite
4 – Fluorite
5 – Apatite
6 – Orthoclase Feldspar
7 – Quartz
8 – Topaz
9 – Corundum
10 – Diamond




Step 1: Identify the mineral corresponding to hardness value 9.

From the Mohs hardness scale, the mineral with a hardness value of 9 is Corundum. Corundum is composed mainly of aluminum oxide (\(Al_2O_3\)) and includes gemstones such as ruby and sapphire.



Step 2: Eliminate other options.


Quartz has hardness 7.
Topaz has hardness 8.
Diamond has hardness 10, the hardest natural mineral.


Thus, the mineral with a Mohs hardness of 9 is Corundum. Quick Tip: Remember the top three minerals in Mohs hardness scale: \textbf{Quartz (7) → Topaz (8) → Corundum (9) → Diamond (10)}. Diamond is the hardest natural mineral.

Concept:

Ecological pyramids represent the trophic structure and energy flow within an ecosystem. There are three main types of ecological pyramids:


Pyramid of Numbers – Shows the number of organisms at each trophic level.
Pyramid of Biomass – Represents the total biomass present at each trophic level.
Pyramid of Energy – Illustrates the flow of energy through different trophic levels.


Energy transfer in ecosystems follows the Second Law of Thermodynamics. During each transfer from one trophic level to the next, a large portion of energy is lost as heat, and only a small fraction (about \(10%\)) is passed on to the next level.



Step 1: Understanding energy flow in ecosystems.

Because energy is continuously lost at each trophic level, the amount of energy available decreases from producers to higher consumers.

Thus, the energy pyramid always has a broad base (producers) and a narrow top (top consumers).



Step 2: Why other pyramids may be inverted.


Pyramid of Numbers can be inverted (e.g., a single tree supporting many insects).
Pyramid of Biomass can be inverted in aquatic ecosystems where phytoplankton biomass is smaller than zooplankton.


However, the Pyramid of Energy can never be inverted because energy always decreases as it moves up the trophic levels. Quick Tip: \textbf{Energy pyramids are always upright}. This is because energy decreases at each trophic level due to heat loss during metabolic processes.

Concept:

The Kyoto Protocol is an international environmental treaty adopted in 1997 in Kyoto, Japan. It was developed under the United Nations Framework Convention on Climate Change (UNFCCC) to address the problem of global warming.

The main objective of the Kyoto Protocol is to reduce the emission of greenhouse gases (GHGs) that contribute to climate change by trapping heat in the Earth's atmosphere.

Major greenhouse gases targeted under the Kyoto Protocol include:


Carbon dioxide (\(CO_2\))
Methane (\(CH_4\))
Nitrous oxide (\(N_2O\))
Hydrofluorocarbons (HFCs)
Perfluorocarbons (PFCs)
Sulfur hexafluoride (\(SF_6\))




Step 1: Identify the purpose of the Kyoto Protocol.

The Kyoto Protocol established legally binding targets for developed countries to reduce their greenhouse gas emissions to combat global warming.



Step 2: Eliminate the other options.


Ozone-depleting gases are regulated under the Montreal Protocol.
Noble gases are chemically inert and not associated with climate change.
Radioactive gases are not the focus of the Kyoto Protocol.


Thus, the Kyoto Protocol primarily aims to reduce the emission of greenhouse gases. Quick Tip: \textbf{Kyoto Protocol → Greenhouse gas reduction → Climate change mitigation.} It set legally binding emission reduction targets for developed countries.

Concept:

Bryophytes are small, non-vascular plants that typically grow in moist and shaded environments. They include plants such as mosses, \textit{liverworts, and \textit{hornworts. These plants lack true roots, stems, and vascular tissues (xylem and phloem).

Bryophytes are often referred to as the "amphibians of the plant kingdom" because although they live on land, they require water for sexual reproduction.



Step 1: Understanding why bryophytes need water.

During fertilization, the male gametes (sperm) of bryophytes are motile and must swim through a thin film of water to reach the female gamete (egg) present in the archegonium.

Thus, the presence of water is essential for successful fertilization.



Step 2: Eliminating other options.


Pteridophytes also require water for fertilization but are vascular plants and are not commonly called amphibians of the plant kingdom.
Gymnosperms reproduce through seeds and pollen; fertilization does not require external water.
Angiosperms are flowering plants where fertilization occurs through pollen tubes and does not require water.


Therefore, the plant group known as the "amphibians of the plant kingdom" is Bryophytes. Quick Tip: \textbf{Bryophytes = Amphibians of the plant kingdom because they live on land but require \textbf{water for fertilization}.

Concept:

The nitrogen cycle describes the movement of nitrogen through the atmosphere, soil, water, and living organisms. Nitrogen undergoes several biological and chemical transformations in this cycle.

Important processes in the nitrogen cycle include:


Nitrogen Fixation – Conversion of atmospheric nitrogen (\(N_2\)) into ammonia (\(NH_3\)) by nitrogen-fixing bacteria.
Nitrification – Conversion of ammonia into nitrites (\(NO_2^-\)) and then nitrates (\(NO_3^-\)).
Ammonification – Conversion of organic nitrogen from dead organisms and wastes into ammonia.
Denitrification – Conversion of nitrates back into nitrogen gas (\(N_2\)) which returns to the atmosphere.




Step 1: Understanding how nitrogen returns to the atmosphere.

The process that releases nitrogen gas back into the atmosphere is denitrification. In this process, certain bacteria convert nitrates (\(NO_3^-\)) present in the soil into nitrogen gas (\(N_2\)) or nitrous oxide (\(N_2O\)).



Step 2: Role of denitrifying bacteria.

Denitrification is carried out by anaerobic bacteria such as Pseudomonas and \textit{Clostridium, especially in waterlogged or oxygen-poor soils.



Step 3: Eliminating other options.


Nitrogen fixation converts atmospheric nitrogen into usable forms.
Nitrification converts ammonia into nitrates.
Ammonification converts organic nitrogen into ammonia.


Thus, the process responsible for returning nitrogen to the atmosphere is denitrification. Quick Tip: \textbf{Denitrification = Nitrates → Nitrogen gas. It is the key step that returns nitrogen back to the atmosphere in the nitrogen cycle.

Concept:

In waste management, leachate refers to the contaminated liquid that forms when water (often rainwater) passes through waste materials in landfills. As the water moves through the waste, it dissolves and carries various chemical substances, organic matter, and pollutants.

Leachate may contain:


Organic compounds
Heavy metals
Toxic chemicals
Microorganisms


Because of these dissolved contaminants, leachate can pose serious risks to soil and groundwater quality if it is not properly managed.



Step 1: Understanding how leachate forms.

When precipitation or surface water infiltrates a landfill, it percolates through the layers of waste and dissolves soluble materials. This process produces a polluted liquid known as leachate.



Step 2: Environmental significance.

Leachate is a major environmental concern in landfill management because it can contaminate nearby groundwater and surface water bodies if not properly collected and treated.



Step 3: Eliminating other options.


Gas released from decomposing waste refers to landfill gas (mainly methane and carbon dioxide).
Solid residue after incineration is known as ash.
Recycled organic compost material refers to compost.


Therefore, leachate is the liquid that drains through waste and carries dissolved contaminants. Quick Tip: \textbf{Leachate = Contaminated liquid formed when water percolates through landfill waste}. Proper landfill liners and treatment systems are used to prevent groundwater contamination.

Concept:

Rat-hole mining is a form of coal mining in which narrow horizontal tunnels are dug into hillsides to extract coal. These tunnels are often very small and unsafe, allowing miners to crawl inside to remove coal manually.

This mining practice is most commonly associated with the state of Meghalaya in northeastern India. The method became controversial due to:


Unsafe working conditions for miners
Frequent mining accidents
Environmental damage
Water pollution due to acid mine drainage


Because of these concerns, the National Green Tribunal (NGT) banned rat-hole mining in Meghalaya in 2014.



Step 1: Identify the state known for rat-hole mining.

Rat-hole mining has been widely practiced in the coal-rich areas of the Jaintia Hills and East Khasi Hills districts of Meghalaya.



Step 2: Eliminate other options.


Jharkhand – Known for large-scale mechanized coal mining.
Odisha – Known for iron ore and bauxite mining.
Chhattisgarh – Major coal and mineral mining but not rat-hole mining.


Thus, the Indian state most associated with the controversial practice of rat-hole mining is Meghalaya. Quick Tip: \textbf{Rat-hole mining} is mainly associated with \textbf{Meghalaya} and was banned by the \textbf{National Green Tribunal (NGT) in 2014} due to environmental and safety concerns.

Concept:

The Environment (Protection) Act is a comprehensive legislation enacted by the Government of India to provide a framework for the protection and improvement of the environment.

The need for this law became urgent after the Bhopal Gas Tragedy of 1984, one of the world's worst industrial disasters. The tragedy exposed serious gaps in environmental safety and industrial regulation in India.

As a response, the Indian government enacted the Environment (Protection) Act in 1986. The Act empowers the central government to take measures to:


Protect and improve environmental quality
Prevent and control pollution
Regulate industrial activities that may harm the environment




Step 1: Understanding the historical context.

The Bhopal Gas Tragedy occurred in 1984 due to the leakage of methyl isocyanate gas from the Union Carbide pesticide plant in Bhopal, Madhya Pradesh.



Step 2: Government response.

To strengthen environmental governance and ensure stricter environmental protection, the government passed the Environment (Protection) Act in 1986.



Step 3: Eliminating other options.


1982 – No major environmental legislation enacted related to the Bhopal disaster.
1984 – Year of the Bhopal Gas Tragedy.
1991 – Associated with economic reforms, not this Act.


Thus, the Environment Protection Act was enacted in 1986. Quick Tip: \textbf{Environment (Protection) Act – 1986} was enacted after the \textbf{Bhopal Gas Tragedy (1984)} to strengthen environmental regulation in India.

Concept:

Itai-Itai disease is a painful condition caused by chronic poisoning from the heavy metal cadmium. The disease was first reported in the Toyama Prefecture of Japan in the early 20th century.

Cadmium pollution occurred due to the release of industrial waste from mining activities into nearby rivers. The contaminated water was used for irrigation, leading to cadmium accumulation in rice crops. Long-term consumption of this contaminated rice caused severe cadmium poisoning in humans.

Cadmium mainly affects the kidneys and bones.



Step 1: Understanding the meaning of "Itai-Itai".

The term “Itai-Itai” in Japanese means “ouch-ouch”, referring to the intense bone pain experienced by patients suffering from the disease.



Step 2: Effects of cadmium poisoning.

Cadmium accumulation in the body leads to:


Severe bone pain
Bone softening (osteomalacia)
Kidney damage
Fragile bones and fractures




Step 3: Eliminating other options.


Mercury causes Minamata disease.
Lead causes lead poisoning affecting the nervous system.
Arsenic causes skin lesions and arsenicosis.


Thus, the heavy metal associated with Itai-Itai disease is Cadmium. Quick Tip: \textbf{Itai-Itai disease → Cadmium poisoning}. Remember: \textbf{Minamata → Mercury}, \textbf{Itai-Itai → Cadmium}.