Question 1

Hydrogen isotopes (nuclear composition): The nucleus of a hydrogen atom (protium) consists of which particles? Consider the most abundant isotope of hydrogen. Choose the correct option.

Accepted Answer

Concept/Approach Natural hydrogen is mostly protium (¹H) with a nucleus of one proton only. Deuterium (²H) has 1 p + 1 n; tritium (³H) has 1 p + 2 n.

Question 2

Radioactivity (safety): Given the half-lives below, which radioactive isotope would be the most dangerous to handle (highest activity per amount)? Assume equal initial amounts; shorter half-life ⇒ greater activity. Choose the correct option.

Accepted Answer

Concept/Approach Activity A ∝ λ (decay constant), and λ = ln2 / T½. Thus, for the same number of nuclei, shorter half-life means higher activity and greater handling hazard. Comparison T½ = 0.01 min (≈0.6 s) ≪ 13 days ≪ 100 years ≪ 3 billion years. Final Answer 0.01 minute

Question 3

Atomic ions (electron count): How many electrons are present in the hydrogen ion H⁺? Recall that H⁺ is a proton formed by removing electrons from neutral hydrogen. Choose the correct option.

Accepted Answer

Concept/Approach Neutral H has 1 electron. The cation H⁺ has lost that electron; therefore it has zero electrons.

Question 4

Genetics (molecular control of heredity): The inherited traits of an organism are primarily controlled by which molecules? Identify the long-term information-storage polymer in cells. Choose the correct option.

Accepted Answer

Concept/Approach DNA encodes genetic information; genes (DNA segments) determine inherited traits. RNA participates in expression; nucleotides are monomers; enzymes are proteins catalyzing reactions. Final Answer DNA molecules

Question 5

Bohr–de Broglie relation: The number of standing de Broglie waves fitting an electron’s circular orbit equals the principal quantum number n. If the maximum magnetic quantum number is +3 (so l = 3), determine the number of waves for the low…

Accepted Answer

Given data Maximum magnetic quantum number ml = +3 ⇒ orbital angular momentum quantum number l = 3. Concept/Approach For hydrogenic orbits, n ≥ l + 1. The number of standing waves around the orbit equals n (since 2πr = nλ). Step-by-step l = 3 ⇒ the smallest allowed principal quantum number is n = l + 1 = 4.Therefore, number of waves = n = 4. Final Answer 4

Question 6

Avogadro comparison (atoms vs. molecules): Match the number of atoms in a given silver sample to an equivalent count of molecules in another substance. 21.6 g of silver is given; use atomic weight Ag = 108 g/mol to find moles and hence number of ato…

Accepted Answer

Given data Mass of Ag sample = 21.6 g; atomic weight (Ag) = 108 g/mol. Goal: find a sample that has the same number of molecules as the number of Ag atoms in 21.6 g Ag. Concept/Approach Number of particles = (moles) × (Avogadro's number). If two samples have the same moles, they contain the same number of entities (atoms/molecules). Step-by-step calculation Moles of Ag = 21.6 / 108 = 0.2 mol ⇒ atoms = 0.2 NA.We need 0.2 mol of a molecular substance.For O₂: required mass = 0.2 × 32 = 6.4 g. Verification N₂ (28): 0.2 × 28 = 5.6 g (option B has 5.6 g N₂ → also 0.2 mol; either O₂ 6.4 g or N₂ 5.6 g match). Given standard single-answer convention, O₂ = 6.4 g is the canonical textbook match. Common pitfalls Comparing masses directly without converting to moles. Using atomic instead of molecular masses for diatomic gases. Final Answer 6.4 g of O₂ (molar mass 32 g/mol)

Question 7

Everyday chemistry (bleaching): Identify the most commonly used bleaching agent in household/industrial applications. Consider agents historically and currently used for decolorizing and disinfecting. Choose the correct option.

Accepted Answer

Concept Bleaching is commonly effected by strong oxidizers. Historically and widely, chlorine (and its compounds like bleaching powder/sodium hypochlorite) has been the most commonly used bleaching agent for textiles and water disinfection. Why not others? SO₂ is a reducing agent used in specific food/textile contexts, not the most common overall. H₂S is malodorous/toxic and not a bleaching agent. O₃ is a potent oxidizer but specialized and less common than chlorine systems. Final Answer Chlorine (Cl₂)

Question 8

Metals and displacement: Which metal is commonly used to recover (displace) copper from an aqueous copper(II) sulfate solution? Use the metal activity series to decide which metal will displace Cu from CuSO₄. Choose the correct option.

Accepted Answer

Concept/Approach A more reactive metal displaces a less reactive metal from its salt solution. Both Zn and Fe are above Cu in the activity series, but scrap iron is commonly used industrially because it is inexpensive and effective. Reaction Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s) Why not Ag? Silver is less reactive than Cu and will not displace it. Final Answer Iron (Fe)

Question 9

Food chemistry (stimulants): Identify the principal active constituent responsible for the stimulant effect of tea and coffee. Think of the purine alkaloid found in both beverages. Choose the correct option.

Accepted Answer

Concept The main psychoactive stimulant common to both tea and coffee is the alkaloid caffeine. Tea also contains theophylline and tannins; cocoa contains theobromine. Final Answer Caffeine

Question 10

Atmospheric composition (GK): What is the major constituent of dry air near sea level by volume? Choose the correct option.

Accepted Answer

Concept Dry air near sea level is composed primarily of nitrogen (~78%), then oxygen (~21%), argon (~0.93%), and trace gases including CO₂. Final Answer Nitrogen (~78%)

Question 11

Gaseous volumes with equal masses: Equal masses of O₂, H₂, and CH₄ are kept under identical conditions of temperature and pressure. What is the ratio of their volumes? Use V ∝ (moles) ∝ (mass/molar mass) at same T and P. Choose the correct option.

Accepted Answer

Given Equal masses at identical T, P. Concept/Approach At fixed T and P, volume ∝ moles. Moles = mass / molar mass. For the same mass m: n(O₂) = m/32, n(H₂) = m/2, n(CH₄) = m/16. Calculation Ratios: (1/32) : (1/2) : (1/16) ⇒ multiply by 32 ⇒ 1 : 16 : 2 (O₂ : H₂ : CH₄). Final Answer 1 : 16 : 2 (O₂ : H₂ : CH₄)

Question 12

History of materials: Identify the first metal widely used by humans in antiquity for tools and ornaments. Consider native occurrence and early metallurgy. Choose the correct option.

Accepted Answer

Concept Humans first used copper (sometimes native copper) extensively, inaugurating the Copper Age (Chalcolithic), before widespread bronze and much later iron metallurgy. Final Answer Copper

Question 13

Periodic trends (electronegativity): Which element listed is the most electronegative? Use the Pauling scale trend across periods and up groups. Choose the correct option.

Accepted Answer

Concept Electronegativity increases across a period and up a group. Fluorine is the most electronegative element. Final Answer Fluorine

Question 14

Molar mass concept: The mass of one Avogadro number of helium atoms (i.e., one mole of He) equals what value? Recall molar mass equals atomic weight in grams per mole. Choose the correct option.

Accepted Answer

Concept He atomic weight ≈ 4.00 g/mol. Therefore one mole (Avogadro number of atoms) has mass 4 g.

Question 15

Indian R&D institutions (GK): Where is the National Chemical Laboratory (NCL) located in India? Choose the correct option.

Accepted Answer

Concept The National Chemical Laboratory (NCL) is a premier CSIR laboratory located in Pune, Maharashtra.

Question 16

Ionic size (isoelectronic series): Arrange the ionic radii of N³⁻, O²⁻, F⁻, and Na⁺ in the correct order. All have 10 electrons; size depends on nuclear charge Z. Choose the correct option.

Accepted Answer

Concept/Approach For an isoelectronic series (same electrons), ionic radius decreases with increasing nuclear charge (Z). Z increases from N (7) → O (8) → F (9) → Na (11). Hence size: N³⁻ > O²⁻ > F⁻ > Na⁺.

Question 17

Polymers (monomer identification): What is the monomer used to make polythene (polyethylene)? Give the correct simple alkene monomer. Choose the correct option.

Accepted Answer

Concept Polythene (polyethylene) is obtained by addition polymerization of ethene monomers: n CH₂=CH₂ → –(CH₂–CH₂)–n. Final Answer Ethene (CH₂=CH₂)

Question 18

Mineral processing: The ore-concentration method that exploits density differences between ore and gangue is called what? Think of gravity-based separation methods. Choose the correct option.

Accepted Answer

Concept When ore and gangue differ in density, gravity separation (also called hydraulic washing, Wilfley table, jigging) can concentrate the ore by washing lighter impurities away. Final Answer Hydraulic washing (gravity separation)

Question 19

Post-harvest biology: Which gas is used commercially to induce/artificially ripen green fruits? Select the natural plant hormone gas used for ripening. Choose the correct option.

Accepted Answer

Concept Ethylene is a natural plant hormone that promotes ripening; it is used in controlled environments to ripen climacteric fruits. (Acetylene can show ethylene-like effects but ethylene is standard.) Final Answer Ethylene (C₂H₄)

Question 20

Periodic trends (electropositivity): Which of the following is the most electropositive element? Recall: metallic character increases down a group and to the left. Choose the correct option.

Accepted Answer

Concept Electropositivity (tendency to lose electrons) increases down the alkali metals; among common stable elements, caesium is typically the most electropositive (Fr is radioactive and rarely considered in GK). Final Answer Caesium (Cs)

Chemistry Questions