Prepare for the UPSC Prelims with our focused collection of topic-wise questions on Chemistry, specifically addressing the Classification of Elements. Dive into the intricate world of element categorization without unnecessary jargon. Explore the periodic table, understanding the principles behind element grouping and trends. Our questions cover essential topics such as the periodic law, periodic trends, and the significance of group and period classifications. With clear and concise explanations, this resource equips you with the knowledge needed to excel in your exam. Whether you’re refreshing your memory or delving into new territory, our comprehensive coverage ensures thorough preparation. Ace the UPSC Prelims confidently with a solid understanding of the Classification of Elements. Empower yourself with our UPSC Prelims Topic Wise Questions – Chemistry – Classification of Elements and pave your path to success.
Q1. The chemical used as a ‘fixer’ in photography is (1995)
(a) sodium sulphate
(b) sodium thiosulphate
(c) ammonium persulphate [(NH4)2S2O8].10H2O
(d) borax Na2B4O7
Ans. (b)
The substance employed as a ‘fixer’ in photography is sodium thiosulfate (Na2S2O3). Photography fixers are compounds or mixtures utilized in the concluding stage of the photographic film process. These fixers stabilize the image, eliminate any unexposed silver halide on the film, and preserve the metallic silver formed in the images, rendering it impervious to subsequent light exposure. Sodium thiosulfate prevents the remaining silver halide from darkening rapidly and causing fogging of the images.
Q2. Which one of the following elements is alloyed with iron to produce steel which can resist high temperatures and also have high hardness and abrasion resistance? (1996)
(a) Aluminium
(b) Chromium
(c) Nickel
(d) Tungsten
Ans. (b)
Chromium is combined with iron to create steel that can withstand high temperatures and possesses high hardness and resistance to abrasion. This alloying element enhances various properties of steel, including tensile strength, hardness, hardenability, toughness, resistance to wear and abrasion, as well as resistance to corrosion and scaling at elevated temperatures.
Q3. The most reactive among the halogens is (1997)
(a) fluorine
(b) chlorine
(c) bromine
(d) iodine
Ans. (a)
Fluorine is the most reactive halogen due to its highly electronegative character and smaller size compared to other halogens. Halogens are located in the 17th group of the periodic table and possess seven electrons in their outermost shell. As we move down the group, the reactivity decreases because the atomic size increases, leading to reduced attraction between the nucleus and electrons. Consequently, it becomes less facile to gain a new electron. The reactivity order of halogen atoms is as follows: F > Cl > Br > I.
Q4. Match list I with list II and select the correct answer using the codes given below the lists. (1998)
| List I | List II |
| A. Potassium bromide | 1. Fertiliser |
| B. Potassium nitrate | 2. Photography |
| C. Potassium sulphate | 3. Bakery |
| D. Monopotassium tartarate | 4. Gun Powder |
Codes
A B C D
(a) 2 4 1 3
(b) 2 4 3 1
(c) 4 2 3 1
(d) 4 2 1 3
Ans. (a)
Potassium bromide (KBr): This compound, along with silver bromide (AgBr), is used in developing photographs from negative films. It enhances the contrast of a photograph, typically a black and white photograph.
Potassium nitrate (KNO3): This compound contains potassium (K), nitrogen (N), and oxygen (O). Upon heating, it releases a significant amount of oxygen. Since oxygen is essential for combustion, the presence of KNO3 in large amounts leads to explosive combustion of other substances. Hence, KNO3 is used in gunpowder.
Potassium sulfate (K₂SO₄): It serves as an excellent source of potassium (K) and sulfur (S), both of which are essential for the growth of plants in substantial quantities. As a result, these two elements are categorized as macronutrients, necessary in large amounts. Consequently, K₂SO₄ finds application in the synthesis of fertilizers.
Monopotassium tartrate (KC4H₂O): Also known as potassium bitartrate or cream of tartar, this compound, along with baking soda (NaHCO3), constitutes the composition of baking powder. It enhances the activity of baking soda, leading to increased puffiness in baked goods.
Q5. Consider the following statements. (1998)
Coke is one of the materials of the charge added to blast furnace for the production of steel/iron. Its function is to
1. act as reducing agent.
2. remove silica associated with the iron ore.
3. function as fuel, to supply heat.
4. act as an oxidising agent.
Select the correct answer using the codes given below.
(a) 1 and 2 are correct
(b) 2 and 4 are correct
(c) 1 and 3 are correct
(d) 3 and 4 are correct
Ans. (c)
Statements (1) and (3) are correct. Coke is considered a reducing agent as it facilitates the reduction of metal oxides. Derived from the incomplete combustion of wood, coke is predominantly composed of nearly pure carbon. The carbon content in coke exhibits a strong affinity for oxygen when combined with metals in the form of metal oxides. Consequently, the metal oxide loses oxygen, a process termed reduction. Additionally, coke serves as a fuel and combusts to generate high temperatures in the furnace.
Q6. Assertion (A) Sodium metal is stored under kerosene. Reason (R) Metallic sodium melts when exposed to air. (1998)
Codes
(a) Both A and Rare true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Ans. (c)
Sodium metal is typically stored in kerosene due to its significant reactivity with both oxygen and moisture. Contrary to popular belief, it does not melt when it reacts with water or air; instead, it forms sodium hydroxide or oxide. Sodium, which belongs to group I and the third period, is classified under the s-block of the periodic table. Its atomic number is 11, and its mass number is 23. Known for its high reactivity, sodium readily reacts with air to produce sodium oxide (Na₂O) and with water to yield sodium hydroxide (NaOH) and hydrogen (H₂). These reactions are highly exothermic, resulting in the generation of substantial heat. Consequently, to mitigate its reactivity with oxygen and moisture, sodium is typically stored submerged in kerosene oil.
Q7. Which one of the following metals does not form amalgams? (1998)
(a) Zinc
(b) Copper
(c) Magnesium
(d) Iron
Ans. (d)
An amalgam constitutes an alloy comprising mercury and another metal (i.e., metal + mercury). While most metals have the capacity to form amalgams with mercury, exceptions exist. Metals such as iron, platinum, tungsten, and tantalum do not typically amalgamate with mercury.
Q8. Match List I (Naturally occurring substances) with List II (Elements) and select the correct answer using the codes given below the lists. (1999)
| List I | List II |
| A. Diamond | 1. Calcium |
| B. Marble | 2. Silicon |
| C. Sand | 3. Aluminium |
| D. Ruby | 4. Carbon |
Codes
A B C D
(a) 3 1 2 4
(b) 4 2 1 3
(c) 2 1 3 4
(d) 4 1 2 3
Ans. (d)
The accurate matching is A-4, B-1, C-2, D-3. Diamond, an allotrope of carbon, represents a phenomenon known as allotropy, where the same element or compound exists in two or more forms possessing similar chemical properties but differing in physical properties. Marble, composed of various constituents including lime (CaO), silica (SiO₂), alumina (Al₂O₃), oxides (Na₂O and MgO), and carbonates (MgCO₃ and others), predominantly contains calcium (Ca). Sand, a mixture of minerals and particles, is chiefly composed of silicon dioxide (SiO₂). Ruby, a pink or blood-red gemstone primarily made up of the mineral corundum or aluminum oxide (Al₂O₃), correctly identifies aluminum from the given elements
Q9. Cobalt-60 is commonly used in radiation therapy because it emits (1999)
(a) α-rays
(b) β-rays
(c) γ-rays
(d) X-rays
Ans. (c)
Cobalt-60 finds widespread application in cancer radiation therapy due to its emission of high-intensity gamma rays (γ-rays) and its comparatively extended half-life compared to other sources of gamma rays with similar intensity. As a synthetic radioactive isotope of cobalt, it possesses a half-life of 5.2714 years.
Q10. Consider the following statements. Glass can be etched or scratched by (1999)
1. diamond
2. hydrofluoric acid
3. aqua-regia
4. conc. sulphuric acid
Which of these statements are correct?
(a) 1 and 4
(b) 2 and 3
(c) 1 and 2
(d) 2 and 4
Ans. (c)
Statements (1) and (2) are correct. Diamond is indeed one of the hardest substances and can be employed to cut or scratch glass. Hydrofluoric acid (HF) is utilized for writing on glass surfaces. Aqua-regia, comprising nitric acid (HNO₃) and hydrochloric acid (HCl) in a molar ratio of 1:3, is a potent solvent. However, aqua-regia and concentrated sulfuric acid (H₂SO₄) are generally unsuitable for etching or scratching glass due to their limited reactivity towards it.
Q11. Assertion (A) To dilute sulphuric acid, acid is added to water and not water to acid. Reason (R) Specific heat of water is quite large. (1999)
(a) Both A and Rare true and R is the correct explanation of A
(b) Both A and R are true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Ans. (a)
Both statements A and R are indeed true, and R provides a correct explanation for A. When diluting sulphuric acid (H₂SO₄), it is essential to add acid to water and not the other way around. This precaution is taken because water possesses a high specific heat capacity, enabling it to absorb the significant amount of heat released during the dilution process. If the reverse procedure is followed and water is added to sulphuric acid, the acid-water reaction can be highly exothermic, causing vigorous boiling and potential splattering, which can result in burns.
Q12. Which of the following substances are found in the beach sands of many parts of Kerala? (2006)
1. Ilmenite
2. Zircon
3. Sillimanite
4. Tungsten
Select the correct answer using the codes given below.
(a) 1, 2, 3, and 4
(b) 1, 2 and 3
(c) 3 and 4
(d) 1 and 2
Ans. (a)
The substances found in the beach sands of many parts of Kerala include ilmenite, zircon, sillimanite, and tungsten. Additionally, heavy mineral sand deposits in Kerala contain rutile, leucoxene, and monazite. Kerala possesses world-class deposits of mineral sands in coastal areas from Neendakara to Kayamkulam.
Q13. Which are the materials generally employed as solder in soldering operations in electronics? (2006)
(a) Iron and tin
(b) Lead and tin
(c) Aluminium and lead
(d) Aluminium and iron
Ans. (b)
Lead and tin are commonly used as solder in electronics. Solder, an alloy of lead and tin (Pb and Sn), typically consists of 40% lead and 60% tin. Its lower melting point compared to pure metals makes it suitable for joining electrical wires.
Q14. Which one of the following does not contain silver? (2007)
(a) Horn silver
(b) German silver
(c) Ruby silver
(d) Lunar caustic
Ans. (b)
Among the given options, only German silver does not contain silver. German silver is an alloy composed of copper (Cu), zinc (Zn), and nickel (Ni). The other options include substances like silver chloride (AgCl), silver nitrate (AgNO3), and red silver.
Q15. Which one among the following is called philosopher’s wool? (2007)
(a) Zinc bromide
(b) Zinc nitrate
(c) Zinc oxide
(d) Zinc chloride
Ans. (c)
Zinc oxide, also known as philosopher’s wool, is utilized in various applications such as face creams and artificial teeth. Its white crystalline powder form, insoluble in water, is also referred to as Chinese white or zinc white.
Q16. What are rubies and sapphires chemically known as? (2008)
(a) Silicon dioxide
(b) Aluminium oxide
(c) Lead tetraoxide
(d) Boron nitride
Ans. (b)
Rubies and sapphires are chemically identified as aluminum oxide. Both gemstones are composed of aluminum oxide (Al2O3), known as corundum. Impurities such as iron, titanium, copper, and chromium impart different colors to these gemstones.
Q17. Which one of the following is also called stranger gas? (2008)
(a) Argon
(b) Neon
(c) Xenon
(d) Nitrous oxide
Ans. (c)
Xenon, also known as stranger gas, was named due to its rarity at the time of discovery. Xenon, along with helium, neon, argon, krypton, and radon, belongs to the noble gases group. These gases, present in minimal amounts in the atmosphere, are sometimes referred to as rare gases.
Q18. Who among the following discovered heavy water? (2008)
(a) Heinrich Hertz
(b) HC Urey
(c) G Mendel
(d) Joseph Priestly
Ans. (b)
Heavy water was discovered by HC Urey, an American physical chemist. Urey’s work on isotopes, particularly his discovery of deuterium, earned him the Nobel Prize in Chemistry in 1934. He also contributed significantly to the development of the atomic bomb.
Q19. Hydrogen fuel cell vehicles produce one of the following as ‘exhaust’ (2010)
(a) NH3
(b) CH4
(c) H₂O
(d) H2O2
Ans. (c)
Hydrogen fuel cell vehicles produce only harmless water vapor (H2O) as exhaust. Hydrogen, used as fuel, reacts with oxygen to produce water vapor as the sole emission.
Q20. The surface of a lake is frozen in severe winter, but the water at its bottom is still liquid. What is the reason? (2011)
( a) Ice is a bad conductor of heat
(b) Since, the surface of the lake is at the same temperature as the air, no heat is lost
(c) The density of water is maximum at 4°C
(d) None of the statements (a), (b) and (c) given above is correct
Ans. (a)
The surface of a lake freezes in severe winter, while the water at its bottom remains liquid. This occurs because ice, being a poor conductor of heat, insulates the water below, preventing it from freezing. As water freezes, it becomes less dense, causing ice to float and form a protective layer on the surface, preventing further cooling of the water below.
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