CBSE Questions for Class 12 Medical Biology Environmental Issues Quiz 6 - MCQExams.com

Substances found in large quantities include epoxy resins, fiberglass, PCBs, PVC (poly vinyl chlorides), thermosetting plastics, lead, tin, copper, silicon, beryllium, carbon, iron and aluminium. Elements found in small amounts include cadmium, mercury and thallium. Elements found in trace amounts include americium, antimony, arsenic, barium, bismuth, boron, cobalt, europium, gallium, germanium, gold, indium, lithium, manganese, nickel, niobium, palladium, platinum, rhodium, ruthenium, selenium, silver, tantalum, terbium, thorium, titanium, vanadium, and yttrium. Almost all electronics contain lead and tin (as solder) and copper (as wire and printed circuit board tracks), through the use of lead-free solder is now spreading rapidly. 

• Electronic waste or e-waste describes discarded electrical or electronic devices. 
• Used electronics which are destined for reuse, resale, salvage, recycling, or disposal are also considered e-waste. 
• E-waste recycling spews dioxins into the air. E-waste recycling using uncontrolled processes is a major source of dioxin related compounds. 
• The air around e-waste recycling areas in Guiyu, China, contains the highest levels of dioxins ever recorded. When computers, televisions, music systems, and other electronic products reach the ends of their lives, they often end up in China or other developing countries as e-waste. 
• Such waste is a serious environmental threat in these parts of the world because of the poorly regulated conditions under which the waste is dismantled. E-waste affects the brain, lungs, and all over the body. There is also evidence of cell membrane lesion, causing DNA single-strand breaks.
• DNA breaks can increase the likelihood of developing cancer. DNA damages are a special problem in non-dividing or slowly dividing cells, where unrepaired damages will tend to accumulate over time. 
• On the other hand, in rapidly dividing cells, unrepaired DNA damages that do not kill the cell by blocking replication will tend to cause replication errors and thus mutation.

• Non-biodegradable substances are substances that cannot be broken down into simple, environmentally safe materials by biological processes. 
• In other words, these substances do not decompose. 
• Nylon in the given options is a synthetic polymer and is nonbiodegradable.

• Solid waste that is generated must be segregated as dry waste and wet waste. This is the best way for the treatment and disposal of waste. 
• Paper is wet waste whereas resin plastic and rubber are dry waste. 

• The waste that is generated from electronic gadgets is called e-waste.
• Several hazardous materials/chemicals are categorized as e-waste like beryllium, Lead, Cadmium, etc. 
• These get deposited in soil for a long period of time causing soil pollution.

• Farming of legumes/grasses and other crops in alternation to improve the soil fertility is called as ley farming. Legumes add nitrogenous compounds to soil and thereby help the soil to resume the lost minerals. This makes option A correct.
• The farming in row patterns that run nearly level around the hill is called as contour farming. Option B is incorrect. 
• Option C is incorrect as strip farming includes dividing the whole field in strips and cultivation in alternate strips to ensure soil fertility. 
• Option D is incorrect as shifting agriculture includes farming in one field and then leaving it for natural vegetation by cultivating in some other field.
  Hence, correct answer is A.

Correct answer: C
Explanation:

• The presence of CFCs in the atmosphere results in the depletion of the ozone layer. The chemical formula of this substance is CF$$_2$$Cl$$_2$$.
• They are used as coolants in refrigerators, coolers, etc.
• The CFCs causes the breaking of the ozone molecule which forms the oxygen radical and O$$_2$$.
• The depletion of the ozone layer results in the penetration of harmful UV radiation from the sun into the Earth's atmosphere.