UGC NTA NET/JRF Exam, Environmental Sciences, June-2023

Al³⁺, pertains to aluminum ions, and it is accurate to assert that aluminum ions do not typically act as proton acceptors in the traditional Brønsted-Lowry acidbase framework.

In aqueous environments, aluminum ions exhibit Lewis acid behaviour by accepting electron pairs in coordination and complexation reactions.

However, their role in proton acceptance is limited, and they are not conventionally involved in transferring protons (H⁺) in acid-base reactions.

Aluminum ions play crucial roles in geochemical processes, often forming complexes with ligands and contributing to the overall chemistry of aquatic systems.

In the formation of photochemical smog in the ambient atmosphere, the species that is not directly involved or required is sulphur dioxide (SO₂).

Photochemical smog primarily arises from the complex interactions between volatile organic compounds (VOCs), nitric oxide (NO), nitrogen dioxide (NO₂), and ozone (O₃) in the presence of sunlight.

Volatile organic compounds, released from various sources such as vehicle exhaust and industrial activities, undergo photochemical reactions in the atmosphere.

However, sulphur dioxide, while a notable air pollutant with its environmental implications, is not a primary contributor to the formation of photochemical smog.

In the context of stratospheric chemistry and ozone depletion, the catalytically inactive (or reservoir) molecule containing chlorine is CIONO₂. Chlorine nitrate is a crucial player in atmospheric processes, acting as a temporary reservoir for reactive chlorine species.

In the stratosphere, where ozone layer depletion occurs, chlorine compounds are implicated in catalytic cycles that lead to ozone destruction.

However, chlorine nitrate is considered inactive because it provides a storage form for chlorine without directly participating in these catalytic ozonedepleting reactions.

Statement I: This statement accurately captures the primary source of sulphur emissions into the atmosphere, which is sulphur dioxide (SO₂). SO₂ is a major emission from various sources, including industrial activities and combustion processes.

The statement then correctly identifies carbonyl sulfide (OCS) as the longest-lived reservoir of sulphur in the atmosphere.

OCS has a longer atmospheric lifetime compared to other sulfur compounds, and it serves as a stable reservoir that participates in the complex sulphur cycle.

Statement II: This statement is also correct, although it simplifies a more complex scenario. Sulphur emissions, primarily in the form of sulphur dioxide, can lead to the formation of sulphate aerosols.

These aerosols have a cooling effect on the climate by reflecting sunlight back into space. Sulphur dioxide, originating from both natural and human-related sources, plays a significant role in the Earth's climate system.

Sulphate aerosols not only directly scatter sunlight but also enhance cloud formation. Sulphate particles act as nuclei around which water can condense, promoting cloud development.

These clouds, seeded by sulphate aerosols, exhibit increased reflectivity, further contributing to the cooling of the planet.

(a) This statement accurately describes the process of coagulation, where destabilization of colloidal particles leads to their aggregation and the formation of larger flocs. Coagulants are added to neutralize the surface charges on colloids, allowing them to come together and form larger, settleable particles.

(b) Brownian motion refers to the random movement of colloidal particles suspended in a fluid medium due to collisions with surrounding molecules. This constant motion is a characteristic feature of colloids and plays a role in their stability.

(c) Colloidal stability is indeed often related to surface charge. Colloids carry a surface charge, preventing them from agglomerating due to electrostatic repulsion. Coagulation involves overcoming this repulsion by adding coagulants (often trivalent cations) to neutralize the charges and allow particles to come closer.

(d) Coagulants are often trivalent cations (charged species with a valence of 3⁺), which can neutralize the negative charges on colloidal particles, leading to coagulation.

Trivalent cations, such as aluminum or iron ions, are commonly used coagulants in water treatment processes. These ions neutralize the negatively charged colloidal particles, promoting their aggregation and forming larger, settleable flocs.

The standard Biochemical Oxygen Demand (BOD) test is a crucial tool in assessing the organic pollution level in water, indicating the amount of dissolved oxygen consumed by microorganisms during the microbial decomposition of organic matter.

In this standardized procedure, a 300 ml BOD bottle is employed, and the test is conducted at a controlled temperature of 20°C over a 5-day incubation period.

This specific set of conditions allows for a consistent and comparable measurement of the biodegradable organic content in water samples.

Statement I: This statement accurately describes the initiation of the phosphorus cycle. Phosphorus, an essential element for life, is released into the environment through the gradual weathering of rocks and minerals.

This process makes phosphorus compounds available in the soil and water, becoming a fundamental source for the subsequent biological uptake by plants and other organisms.

Statement II: This statement is false. In the context of the phosphorus cycle, plants (producer organisms) predominantly absorb inorganic phosphorus, particularly as phosphate ions (PO₄³⁻), from the soil.

While organic forms of phosphorus do exist, such as in organic matter and decaying organic material, plants typically assimilate inorganic phosphate for their metabolic processes and growth.

Lead (Pb) is conspicuously absent from the repertoire of metals commonly employed in wood preservatives. Wood preservatives play a crucial role in protecting wood from decay, insect infestation, and environmental degradation.

While copper (Cu), chromium (Cr), and arsenic (As) are frequently utilized metals in wood treatment formulations, lead is notably excluded. The decision to omit lead from wood preservatives is rooted in its well-documented toxicity, posing significant risks to both human health and the environment.

The Redundancy Hypothesis represents a nuanced perspective on the intricate interplay between biodiversity and ecosystem functioning.

At its core, this hypothesis contends that ecosystems possess a degree of resilience against species loss when there is functional redundancy, emphasizing the redundancy of ecological roles or functions among different species.

In essence, if one species providing a specific function is lost due to factors like disturbances or environmental changes, another species with analogous functional traits can step in to fulfill that role.

This redundancy in functional traits across diverse species acts as a safety net, maintaining overall ecosystem functionality even in the face of biodiversity changes.