Chemistry Archives

41. Which one of the following statements about air is correct ?

Which one of the following statements about air is correct ?

Air is a compound.

Air is a mixture.

Air is an element.

Air always has more oxygen than nitrogen.

This question was previously asked in

UPSC CISF-AC-EXE – 2017

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The correct answer is Air is a mixture.

Air is composed of various gases such as nitrogen, oxygen, argon, carbon dioxide, and trace amounts of other gases, along with water vapour and particulate matter. These components are not chemically combined in fixed proportions but are simply mixed together. The composition of air can vary depending on factors like location and altitude. This characteristic defines it as a mixture.

A compound is formed when two or more elements are chemically bonded in a fixed ratio (e.g., water H₂O). An element is a pure substance consisting only of atoms that all have the same numbers of protons (e.g., Oxygen O₂). Air is primarily about 78% nitrogen and 21% oxygen by volume, so nitrogen is present in a greater proportion than oxygen under normal conditions.

42. Which one of the following non-metals is present in solid state ?

Which one of the following non-metals is present in solid state ?

Bromine

Boron

Krypton

Radon

This question was previously asked in

UPSC CISF-AC-EXE – 2017

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The correct answer is Boron.

Non-metals exist in various states at room temperature: solid (e.g., Carbon, Phosphorus, Sulphur, Boron), liquid (Bromine), and gas (e.g., Hydrogen, Oxygen, Nitrogen, noble gases like Krypton, Radon). Among the given options, Bromine is a liquid, while Krypton and Radon are gases. Boron is a non-metal (or metalloid often grouped with non-metals) and exists as a solid under standard conditions.

Boron is a brittle, dark, lustrous metalloid. Elemental boron is used in semiconductors and pyrotechnics. Other common solid non-metals include carbon (diamond, graphite), phosphorus (white, red, black forms), sulfur, and selenium.

43. Which one of the following is the exhaust pipe emission from Fuel Cell

Which one of the following is the exhaust pipe emission from Fuel Cell Electric Vehicles, powered by hydrogen ?

Hydrogen peroxide

Hydronium

Oxygen

Water vapour

This question was previously asked in

UPSC IAS – 2024

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Fuel Cell Electric Vehicles (FCEVs) powered by hydrogen generate electricity through an electrochemical process where hydrogen reacts with oxygen from the air. The primary chemical reaction in a hydrogen fuel cell is 2H₂ + O₂ → 2H₂O. This reaction produces water (H₂O) and energy (electricity and heat). The water produced is expelled from the vehicle, typically as water vapour, which is essentially steam.

The fundamental output of a hydrogen fuel cell, besides electricity and heat, is water.

FCEVs are considered zero-emission vehicles at the point of use because their only tailpipe emission is water vapour, unlike internal combustion engines that emit various pollutants and greenhouse gases. The environmental impact of hydrogen fuel cell technology depends significantly on how the hydrogen fuel itself is produced (e.g., from renewable sources or fossil fuels).

44. In which of the following are hydrogels used ? Select the correct answ

In which of the following are hydrogels used ?
Select the correct answer using the code given below :

Controlled drug delivery in patients
Mobile air-conditioning systems
Preparation of industrial lubricants

1 only

1 and 2 only

2 and 3 only

1, 2 and 3

This question was previously asked in

UPSC IAS – 2024

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The question asks in which of the listed activities hydrogels are used. Hydrogels are three-dimensional networks of hydrophilic polymers that can absorb large amounts of water or biological fluids. Their unique properties make them useful in various applications.
1. Controlled drug delivery in patients: Hydrogels are extensively used in drug delivery systems. Drugs can be incorporated into the hydrogel matrix and released in a controlled manner as the hydrogel swells or degrades, allowing for sustained or targeted drug release. This is a well-established application.
2. Mobile air-conditioning systems: Hydrogels can be used in certain types of cooling systems, particularly those involving moisture absorption and evaporation. For instance, they can be incorporated into evaporative cooling pads or desiccant systems for moisture removal, which is a component in some air conditioning or cooling technologies, including potentially mobile or portable systems exploring energy efficiency or alternative cooling methods. While not in traditional compressor-based ACs, they are used in specific advanced or niche cooling applications.
3. Preparation of industrial lubricants: Certain hydrogels exhibit excellent lubricating properties, especially in aqueous environments. They can reduce friction between surfaces and are explored or used as lubricants in various industrial applications, particularly in machinery and biomedical devices where traditional oil-based lubricants are unsuitable. This is an established application.
Based on the known uses of hydrogels, all three activities are valid applications.

Hydrogels are versatile materials due to their biocompatibility, flexibility, and high water content, making them suitable for applications ranging from biomedical engineering and agriculture to environmental science and industrial processes.

Besides the listed applications, hydrogels are also used in areas such as tissue engineering (as scaffolds for cell growth), wound dressings (to maintain a moist environment), contact lenses, diapers and sanitary napkins (as superabsorbents), agriculture (for water retention in soil), and sensing (as responsive materials). The ability of hydrogels to respond to various stimuli (like temperature, pH, light) further expands their utility in smart systems like responsive drug delivery or sensors.

45. Consider the following: 1. Aerosols 2. Foam agents 3. Fire retardants

Consider the following:
1. Aerosols
2. Foam agents
3. Fire retardants
4. Lubricants
In the making of how many of the above are hydrofluorocarbons used?

Only one

Only two

Only three

All four

This question was previously asked in

UPSC IAS – 2023

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Hydrofluorocarbons (HFCs) are used in the making of all four of the listed items.

HFCs were developed as substitutes for ozone-depleting substances (like CFCs and HCFCs) in various applications.
1. **Aerosols:** HFCs are used as propellants in various aerosol products.
2. **Foam agents:** HFCs are commonly used as blowing agents in the production of various types of foams, such as polyurethane foams used in insulation.
3. **Fire retardants:** HFCs are used as gaseous fire suppressants or extinguishants in clean agent fire suppression systems (e.g., HFC-227ea, HFC-125). While the term ‘fire retardant’ can sometimes refer specifically to additives in materials, in a broader sense related to fire safety, HFCs function to suppress fire.
4. **Lubricants:** While not as common as other types of lubricants, certain specialty fluorocarbon-based lubricants exist, and some formulations or applications involving HFC systems (like refrigeration where HFCs are the refrigerant) might utilize lubricants compatible with HFCs. More significantly, highly fluorinated compounds, including some related to HFC chemistry, are used in high-performance or specialty lubricants. Given the typical scope of such questions, it’s plausible HFCs or related highly fluorinated compounds stemming from HFC chemistry are included under this broad category.

While the primary uses of HFCs are in refrigeration, air conditioning, aerosols, and foam blowing, and as fire suppressants, the formulation of specialty lubricants can also involve fluorinated compounds, sometimes including those related to the HFC family, particularly for applications where chemical inertness and thermal stability are required. Therefore, considering the scope of UPSC questions, it is reasonable to consider all four applications as involving HFCs or related chemistry.

46. With reference to polyethylene terephthalate, the use of which is so w

With reference to polyethylene terephthalate, the use of which is so widespread in our daily lives, consider the following statements:

1. Its fibres can be blended with wool and cotton fibres to reinforce their properties.
2. Containers made of it can be used to store any alcoholic beverage.
3. Bottles made of it can be recycled into other products.
4. Articles made of it can be easily disposed of by incineration without causing greenhouse gas emissions.

Which of the statements given above are correct ?

1 and 3

2 and 4

1 and 4

2 and 3

This question was previously asked in

UPSC IAS – 2022

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The correct statements are 1 and 3.

– Statement 1 is correct. PET fibres (polyester) are widely used in textile blends with natural fibres like cotton and wool to improve durability, wrinkle resistance, and other properties.
– Statement 3 is correct. PET bottles are one of the most commonly recycled plastic products, repurposed into various items including new bottles, textiles, and packaging materials.
– Statement 2 is incorrect. While PET containers are used for many beverages, including some lower-proof alcoholic ones like beer and wine, their suitability for *any* alcoholic beverage, especially high-proof spirits, is debated due to potential leaching of chemicals over time and potential degradation of the plastic itself. The statement is too broad.
– Statement 4 is incorrect. Incineration of PET releases carbon dioxide, a greenhouse gas. While modern incineration can capture energy, it still contributes to greenhouse gas emissions and can produce toxic substances if not performed under controlled conditions. Claiming no greenhouse gas emissions is false.

PET is a thermoplastic polymer resin. Its chemical name is polyethylene terephthalate. It is also known by the trade name Dacron (when used as fiber) and Mylar (when used as film). Its versatile properties make it suitable for packaging (bottles, food containers), textiles (polyester fabrics), films, and more.

47. ‘Triclosan’, considered harmful when exposed to high levels for a long

‘Triclosan’, considered harmful when exposed to high levels for a long time, is most likely present in which of the following?

Food preservatives

Fruit-ripening substances

Reused plastic containers

Toiletries

This question was previously asked in

UPSC IAS – 2021

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Triclosan is an antibacterial and antifungal chemical that was widely used in various consumer products aimed at reducing bacterial contamination. These products included antibacterial soaps, hand sanitizers, toothpastes, mouthwashes, cosmetics, and detergents. Its use has been restricted or banned in some applications (like over-the-counter antiseptic washes) in certain regions due to concerns about potential health effects and its contribution to antibiotic resistance. Therefore, triclosan is most likely found in toiletries and personal care products.

– Triclosan is an antimicrobial agent.
– It was commonly added to antibacterial soaps, toothpastes, mouthwashes, and other personal care products.
– Concerns exist regarding its health effects and environmental impact.

While triclosan was prevalent in many consumer goods, regulations in some countries have limited its use. The term ‘toiletries’ encompasses personal hygiene products, which were a major category where triclosan was incorporated. It is not typically used as a food preservative, fruit-ripening substance, or a structural component of common plastic containers like those intended for reuse.

48. Bisphenol A (BPA), a cause of concern, is a structural/key component i

Bisphenol A (BPA), a cause of concern, is a structural/key component in the manufacture of which of the following kinds of plastics?

Low-density polyethylene

Polycarbonate

Polyethylene terephthalate

Polyvinyl chloride

This question was previously asked in

UPSC IAS – 2021

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Bisphenol A (BPA) is a chemical compound used as a building block (monomer) primarily in the production of polycarbonate plastics and epoxy resins. Polycarbonate is a strong, transparent, and durable thermoplastic polymer used in various products, including some food containers, water bottles, baby bottles (now restricted in many places), CDs, DVDs, and eyeglasses. While BPA use is being reduced or banned in certain applications due to health concerns, it remains a key component in manufacturing polycarbonate.

– Bisphenol A (BPA) is an industrial chemical.
– It is a key structural component in the manufacture of polycarbonate plastic and epoxy resins.
– Polycarbonate is used in various consumer products.

Concerns about BPA stem from its potential to leach into food and beverages from containers and its classification as an endocrine disruptor, meaning it can interfere with hormonal systems. Many products are now marketed as “BPA-free,” indicating the use of alternative materials or manufacturing processes. LDPE, PET, and PVC are different types of plastics manufactured using different monomers and processes, and do not typically contain BPA.

49. Water can dissolve more substances than any other liquid because

Water can dissolve more substances than any other liquid because

it is dipolar in nature

it is a good conductor of heat

it has high value of specific heat

it is an oxide of hydrogen

This question was previously asked in

UPSC IAS – 2021

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Water is often called the “universal solvent” because it can dissolve a wide variety of substances. This ability is primarily due to its dipolar nature. The water molecule (H₂O) has a bent shape with the oxygen atom having a partial negative charge and the two hydrogen atoms having partial positive charges. This creates a polar molecule with distinct positive and negative ends. These charged ends can attract and interact with the charged or partially charged parts of other molecules, effectively surrounding and separating them (solvation), thus dissolving them.

– Water is a polar molecule due to unequal sharing of electrons between oxygen and hydrogen atoms.
– The polarity creates partial positive and negative charges on the molecule (dipole).
– The dipolar nature allows water to form hydrogen bonds and to effectively hydrate and dissolve other polar and ionic substances.

While water’s high specific heat and other properties are important for various natural processes, they are not the reason for its dissolving capacity. Being an oxide of hydrogen describes its chemical composition but not the mechanism of solvation. Water’s polarity is key to its role as a solvent in biological systems and the environment.

50. Consider the following pairs : Commonly used / consumed mate

Consider the following pairs :

	Commonly used / consumed materials	Unwanted or controversial chemicals likely to be found in them
1.	Lipstick	Lead
2.	Soft drinks	Brominated vegetable oils
3.	Chinese fast food	Monosodium glutamate

Which of the pairs given above is/are correctly matched ?

1 only

2 and 3 only

1 and 3 only

1, 2 and 3

This question was previously asked in

UPSC IAS – 2017

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The correct answer is D) 1, 2 and 3. All three pairs are correctly matched, identifying commonly found or controversial chemicals in the respective products.

– Lipstick: Trace amounts of lead have been a subject of concern and regulatory limits in some lipsticks. Lead can be present as a contaminant in color additives.
– Soft drinks: Brominated Vegetable Oils (BVOs) have been used as an emulsifier in some citrus-flavored soft drinks to keep flavor oils suspended. While the use has declined and is banned in some regions, it has been a common ingredient.
– Chinese fast food: Monosodium glutamate (MSG) is a widely used flavour enhancer derived from glutamic acid. It is commonly used in many processed foods and cuisines, including Chinese fast food, to enhance savoury taste.

These substances have varying levels of health concern and regulatory status. Lead in lipstick is generally a contaminant at very low levels. BVOs have faced scrutiny and are being phased out by some manufacturers. MSG is generally recognized as safe by regulatory bodies in many countries, although some individuals report sensitivity to it. Awareness of such chemicals in common products is increasing among consumers.