Chemistry (Part-II) (UPSC)

Total Questions: 56

31. Consider the following statements : [2012-I]

Chlorofluorocarbons, known as ozone-depleting substances, are used

1. In the production of plastic foams
2. In the production of tubeless tyres
3. In cleaning certain electronic components
4. As pressurizing agents in aerosol cans

Which of the statements given above is/are correct?

Correct Answer: (c) 1, 3 and 4 only
Solution:Chlorofluorocarbons are used in the production of plastic foams, in cleaning electronic components and as pressurizing agents in aerosol cans. CFCs are non-toxic, non-flammable and very stable, which makes them ideal for use in appliances in private households.
However, the atmospheric impacts of CFCs are not limited to their role as ozone-depleting chemicals. Infrared absorption bands prevent heat at that wavelength from escaping the earth's atmosphere. CFCs have their strongest absorption bands from C-F and C-Cl bonds in the spectral region of 7.8-15.3 µm-referred to as "atmospheric window" due to the relative transparency of the atmosphere within this region.
The strength of CFC absorption bands and the unique susceptibility of the atmosphere at wavelengths where CFCs (indeed all covalent fluorine compounds) absorb creates a "super" greenhouse gas (GHG) effect from CFCs and other unreactive fluorine-containing gases such as perfluorocarbons, HFCS, HCFCs, bromofluorocarbons.

32. With reference to the usefulness of the by-products of sugar industry, which of the following statements is/are correct? [2013-I]

1. Bagasse can be used as biomass fuel for the generation of energy.
2. Molasses can be used as one of the feedstocks for the production of synthetic chemical fertilizers.
3. Molasses can be used for the production of ethanol.

Select the correct answer using the codes given below.

Correct Answer: (c) 1 and 3 only
Solution:Bagasse is often used as a primary fuel source as it produces sufficient heat energy. Molasses can be used for the production of Ethanol. Ethanol is produced by the age old technique of fermentation of cereals, grams, molasses and other materials with high starch contents. Molasses is an inexpensive and readily available raw material.

Molasses cannot be used as a synthetic fertilizer as molasses contain calcium, magnesium and Iron where as synthetic fertilizers are comprised of NPK i.e. Nitrogen, Phosphorous and Potassium.

33. In the context of the proposals to the use of hydrogen-enriched CNG (H-CNG) as fuel for buses in public transport, consider the following statements [2019-I]

1. The main advantage of the use of H-CNG is the elimination of carbon monoxide emissions.
2. H-CNG as fuel reduces carbon dioxide and hydrocarbon emissions.
3. Hydrogen up to one-fifth by volume can be blended with CNG as fuel for buses.
4. H-CNG makes the fuel less expensive than CNG.

Which of the statements given above is/are correct?

Correct Answer: (b) 2 and 3 only
Solution:
  • Compared to conventional CNG, use of H-CNG can reduce emissions of carbon monoxide up to 70% so #1 is wrong, because it doesn't 'eliminate CO emission'.
  • Same Indian Express article reads: For consumers who pay Rs 42 per kg for CNG, the cost of H-CNG would not be more than Rs 43 per kg. NITI Aayog-CII Action Plan for Clean Fuel notes that physical blending of CNG and hydrogen involves a series of energy-intensive steps that would make H-CNG more expensive than CNG. So, #4 is wrong. By elimination we are left with answer B: only 2 and 3.

Do not confuse yourself with LPG and CNG. LPG's primary component is propane and butane while CNG's is methane. The full form of LPG is Liquefied petroleum gas which is used as a fuel in cooking equipment, vehicle and heating appliances.

34. The term 'West Texas Intermediate', sometimes found in news, refers to a grade of [2020-I]

Correct Answer: (a) Crude oil
Solution:WTI is associated with crude oil trade in USA.
Crude oil is a naturally occurring petroleum product composed of hydrocarbon deposits and other organic materials. A type of fossil fuel, crude oil is refined to produce usable products including gasoline, diesel, and various other forms of petrochemicals. It is a nonrenewable resource, which means that it can’t be replaced naturally at the rate we consume it and is, therefore, a limited resource.
Crude oil is the raw natural resource that is extracted from the earth and refined into products such as gasoline, jet fuel, and other petroleum products

35. Consider the following: [2023-I]

1. Aerosols
2. Foam agents
3. Fire retardants
4. Lubricants

In the making of how many of the above are hydrofluorocarbons used?

Correct Answer: (c) Only three
Solution:
  • The answer is (c), only three.
  • Hydrofluorocarbons (HFCs) are man-made chemicals that are used in a variety of products, including aerosols, foam agents, and fire retardants. HFCs are also used as refrigerants, but they are being phased out in many countries due to their environmental impact.
  • HFCs are not used in the making of lubricants. Lubricants are typically made from petroleum-based products or synthetic oils.
  • Therefore, the correct answer is (c), only three.

36. Consider the following statements: [2023-I]

1. Carbon fibres are used in the manufacture of the components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.

Which of the statements given above is/are correct?

Correct Answer: (a) 1 only
Solution:The correct answer is (a).St 1 is right: Carbon Fibre is an important raw material for structural applications in defence, automobile aerospace and nuclear technologies. Technology can be used extensively in wind turbines and deep well oil explorations.. St 2 is wrong, they can be recycled.
  • Carbon Fibre is a new-age material which has found multiple uses in industry and automotive sector. It is a lightweight but strong material with high conductivity and has been growing in demand as a substitute for steel in the auto mobile, construction and military sectors.
  • Recently, Reliance Industries chairman Mukesh Ambani at the 45th AGM announced the company's plan to build India's 1st and World's Largest Carbon Fibre Plant at Hazira, Gujarat.

37. The final Agent Orange raid in Vietnam took place in 1970-areas have begun to bloom again. But 19 years after the war's end, it seems plain that Agent Orange is killing and maiming human beings, something it never intended to do. The apparent toxic fallout from those clouds-is a crop of human miseries including cancers, miscarriages and birth defects-that may persist for decades." [1995]

The offensive substance referred to in this quotation is:

Correct Answer: (d) Dioxin used as defoliants
Solution:America used Dioxin which is defoliants to clear the forests of Vietnam, so that is could kill the Vietnamese guerilla hiding in the forest. But the Dioxin had many after effects like cancers, miscarriage, and birth defects in after years.

38. Which one of the following fuels causes minimum environmental pollution ? [1995]

Correct Answer: (c) Hydrogen
Solution:Except hydrogen, all the rest three options diesel, coal and kerosene are either naturally occurring fossil fuels or derived from them. Thus as we know naturally occuring fossil fuels and their products have high percentage of carbon which on combustion lead to discharge of oxides by carbon (CO₂ & CO) in air. This results in to heavy environmental pollution like CO₂ results in to green house effect causes global warming While CO is poisonous in nature, it combines with hemoglobin of blood to form carboxyhemoglobin. Hydrogen fuel as such causes no pollution because on combustion with oxygen it forms water that's why it is also called future fuel.

39. Physico-chemical characteristics of water in water sources undergo changes due to [1996]

Correct Answer: (c) effluents
Solution:Aquatic macrophytes, aquatic fungi are natural organism and evapotranspiration is a natural process by which plant losses water. Thus being natural they do not results into any change in physico-chemical characteristics of water while effluents discharged into water bodies by industrial units and domestic sewage results in to change in physico-chemical characteristics like pH, conductivity, temperature, electrical conductivity, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, NH₄⁺ and NO₃⁻ ion contents etc.

40. The water pollution in river is measured by the dissolved amount of [1998]

Correct Answer: (d) Oxygen
Solution:Water pollution in river or any other water body is measured by amount of dissolved oxygen. Water pollution can be measured on the basis of parameters like dirtyness, change in texture, total suspended solid and other important factors like,

1. Decrease in dissolved oxygen (DO) (concentration of dissolved oxygen in water samples).
2. Increase in BOD, (Biochemical Oxygen Demand) it is a chemical procedure for determining the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period.
3. Increase in COD, (Chemical Oxygen Demand) test is commonly used to indirectly measure the amount of organic compounds in water.