NEET Environmental Issues Previous Year Questions with Solutions

One Dobson Unit ($1\text{ DU}$) is defined as the thickness of a pure layer of ozone that would be formed if the entire atmospheric ozone column were compressed to Standard Temperature and Pressure ($STP: 0^\circ\text{C}, 1\text{ atm}$):

NCERT states verbatim: "The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU)."

Kilobase is a genetic measurement ($10^3\text{ bp}$ of DNA). Decibel ($dB$) measures acoustic sound pressure level ($>150\text{ dB}$ damages eardrums). Decameter is an SI distance unit ($10\text{ m}$).

Runoff of domestic sewage and agricultural fertilizers introduces excessive nitrogen and phosphorus into water bodies (cultural eutrophication), inducing explosive proliferation of planktonic algae:

NCERT states verbatim: "Presence of large amounts of nutrients in waters also causes excessive growth of planktonic (free-floating) algae, called an algal bloom. Algal blooms impart a distinct colour to the water bodies. Algal blooms cause deterioration of the water quality and fish mortality. Some bloom-forming algae are extremely toxic to human beings and animals."

Statement (1) accurately defines biomagnification (e.g., DDT and mercury). Statement (2) accurately describes biochemical oxygen demand (BOD) and suffocating hypoxia. Statement (4) accurately describes the "Terror of Bengal" ($\textit{Eichhornia crassipes}$).

An electrostatic precipitator operates by maintaining electrode wires at thousands of volts to produce a corona discharge that releases electrons. Electrons attach to dust particles, giving them a net negative charge so that grounded collecting plates attract and capture them:

NCERT states verbatim: "There are several ways of removing particulate matter; the most widely used of which is the electrostatic precipitator, which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant." Statement I is TRUE.

Ionizing radiations (alpha, beta, gamma rays) are nuclear emissions managed via thick lead shielding and deep geological disposal of nuclear wastes. ESPs have zero capability to neutralize radiation. Statement II is FALSE.

Non-biodegradable lipophilic toxicants (such as DDT and mercury) cannot be metabolized or excreted by organisms and get passed to higher trophic levels, progressively concentrating up the food web:

NCERT states verbatim: "Biomagnification refers to increase in concentration of the toxicant at successive trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted, and is thus passed on to the next higher trophic level."

Algal blooms cause hypoxia that sharply *increases* fish mortality (ruling out Option 1). Eutrophication is the *natural or accelerated nutrient enrichment aging* of a lake (ruling out Option 2). High nutrients *stimulate* explosive algal blooms rather than restricting them (ruling out Option 4).

The concentration and total thickness of the stratospheric ozone ($O_3$) layer in a vertical column extending from Earth's surface to outer space is measured in Dobson Units (DU), named after Gordon Dobson, who designed the first spectrophotometer to measure total column ozone. - One Dobson Unit represents a layer of pure ozone gas that would be $10\,\mu\text{m}$ ($0.01\text{ mm}$) thick under standard temperature and pressure ($0^\circ\text{C}$ and $1\text{ atm}$).

Normal stratospheric ozone thickness ranges between 300 to 400 DU. A drop below 220 DU over the Antarctic continent is conventionally defined as the seasonal "ozone hole" caused by chlorofluorocarbons (CFCs).

Recognizing the deleterious effects of ozone depletion over the Antarctic stratosphere caused by chlorofluorocarbons (CFCs), an international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (and became effective in 1989).

The explicit goal of the Montreal Protocol was to control and phase out the emission of ozone depleting substances (ODSs) globally.

Kyoto Protocol (1997) is aimed at reducing greenhouse gas emissions to combat climate change; Cartagena Protocol regulates transboundary movements of Living Modified Organisms (GMOs); Basel Convention regulates hazardous waste disposal.

Option (2) directly captures the mandated objective of the Montreal Protocol.

UV radiation from the sun is categorized into UV-C, UV-B, and UV-A. UV-C is absorbed by the atmosphere; UV-B is largely absorbed by the stratospheric ozone shield. Thinning of the ozone layer over Antarctica allows excessive UV-B to penetrate to the surface.

NCERT explicitly states: "In human eye, cornea absorbs UV-B radiation, and a high dose of UV-B causes inflammation of cornea, called snow-blindness, cataract, etc. Such exposure may permanently damage the cornea."

- Option (1) claims freezing of fluids: Antarctic temperatures are cold, but eye fluids do not freeze while alive. - Option (3) claims reflection of visible light from snow: Snow reflects UV-B, but the direct cause of blindness is the corneal inflammation induced by UV-B, not mere visible light reflection. - Option (4) mentions infra-red damage to retina: Snow blindness involves UV-B damage to the CORNEA, not IR damage to the retina.

Option (2) precisely articulates the medical definition and NCERT explanation of snow-blindness.