CBSE Class 12 Biology Exemplar NCERT Solutions Chapter 16: Environmental Issues

Pollutants can be classified based on their ability to degrade naturally. Biodegradable pollutants are broken down quickly by biological processes, while non-biodegradable pollutants degrade very slowly or not at all.

Non-biodegradable pollutants include materials like plastics, tin containers, heavy metals, and radioactive substances. These are predominantly created by human activities, particularly through industrialization and modern consumption patterns. Nature and natural disasters do not generate these types of persistent pollutants.

Therefore, the correct answer is (c) humans, as they are the primary creators of non-biodegradable pollutants.

Air pollutants encompass gaseous materials, radioactive substances, and particulate matter. The impact of particulate matter on health is largely dependent on its size.

Particulate pollutants can be categorized as settable (10 μm or larger) and suspended (less than 10 μm). According to the Central Pollution Control Board (CPCB), particulate matter with a diameter of 2.50 micrometers or less ($PM\_\{2.5\}$) poses the greatest risk to human health.

These fine particles can be inhaled deep into the respiratory tract, reaching the lungs. Their presence can lead to various respiratory problems and, in severe cases, may even be fatal. Thus, the correct option is (a) 2.50 micrometers.

Soundproofing involves using materials that can absorb sound effectively to prevent echoes and reduce noise transmission. Materials used for this purpose need to have sound-absorbing properties.

Styrofoam is a lightweight, porous material that is excellent at absorbing sound waves. This makes it a suitable choice for soundproofing applications in spaces like recording studios, cinema halls, and auditoriums, where acoustic quality is crucial.

While materials like cotton and wood can offer some sound insulation, styrofoam is particularly effective for sound absorption in these professional settings. Earplugs, used in noisy industrial environments, are often made from fine glass wool or cotton wool, and ear muffs utilize fluid seals or plastic foam for sound absorption.

Therefore, the material generally used for soundproofing rooms like recording studios and auditoriums is (d) styrofoam.

Compressed Natural Gas (CNG) is widely used as a cleaner and more economical fuel, often replacing petrol and diesel. Its environmental advantage stems from its composition.

CNG primarily consists of methane ($CH\_4$), typically making up around 90% of the gas. It is produced by compressing natural gas to less than 1% of its standard atmospheric pressure volume.

Propane and butane are the main components of Liquefied Petroleum Gas (LPG). Ethane is primarily used in the chemical industry for producing ethene.

Therefore, the main component of CNG is (b) methane.

Eichhornia, commonly known as water hyacinth, is an aquatic plant that has become a significant environmental problem in many parts of the world. While it was introduced to India with the intention of absorbing pollutants like mercury, cadmium, and lead from sewage water, its rapid and uncontrolled growth has led to severe ecological issues.

As an invasive species, Eichhornia can quickly cover entire ponds and lakes, blocking sunlight from reaching submerged plants, disrupting water flow, and reducing dissolved oxygen levels. It also provides a habitat for disease vectors like mosquitoes and hosts for parasites like flatworms.

Due to its aggressive growth and detrimental impact on aquatic ecosystems, Eichhornia is widely considered the world's most problematic aquatic weed. The other options, Azolla, Wolffia, and Trapa, are also aquatic plants but do not pose the same level of global ecological threat as Eichhornia.

Therefore, the correct answer is (c) Eichhornia.

Biomagnification, also referred to as bioamplification or ecological magnification, is the process by which the concentration of certain substances increases in organisms at successively higher trophic levels in a food chain. This typically occurs with non-biodegradable and toxic materials.

Substances like Mercury (Hg) and DDT (Dichloro diphenyl trichloroethane) are persistent organic pollutants that are not easily metabolized or excreted by organisms. As a result, they accumulate in the tissues of organisms and their concentration increases as they move up the food chain, potentially reaching toxic levels in top predators.

Sulfur dioxide ($SO\_2$) is an air pollutant primarily associated with acid rain and respiratory issues. It does not typically biomagnify in the same manner as heavy metals or persistent organic pollutants.

Therefore, both Mercury and DDT are known to cause biomagnification. The correct option is (d) Both (b) and (c).

DDT is a synthetic organochlorine insecticide that was widely used for pest control in the mid-20th century. Its chemical name is quite specific and relates to its molecular structure.

The expanded form of DDT is dichloro diphenyl trichloroethane. It was first synthesized in 1874 and became prominent for its effectiveness against insect vectors of diseases like malaria and typhus. However, due to its persistence in the environment and potential harm to wildlife (especially birds) and human health, its use has been banned or severely restricted in most countries since the 1970s.

The other options represent incorrect chemical names.

Therefore, the correct expanded form of DDT is (a) dichloro diphenyl trichloroethane.