Q35. Which chemical weathering process occurs when atmospheric or soil carbon dioxide dissolves in water?
[RRB NTPC Graduate Level CBT-II, 10 July 2026]
(A) Carburation
(B) Carbolation
(C) Carboxylation
(D) Carbonation
Answer: (D) Carbonation
Explanation: Carbon dioxide reacts with water to form weak carbonic acid. This acid attacks carbonate minerals, especially limestone, producing more soluble bicarbonates. The chemical weathering process involving carbonic acid formation and its attack on rocks is called carbonation.
Q34. What property of noble gases accounts for their very low chemical reactivity under standard conditions?
[RRB NTPC Undergraduate CBT-I, 20 June 2026, Shift 2]
(A) Completely filled valence shell
(B) High atomic mass
(C) High electronegativity
(D) Low ionization energy
Answer: (A) Completely filled valence shell
Explanation: Noble gases have stable outer electron shells. Helium contains two electrons in its first shell, while most other noble gases possess eight valence electrons. Their filled shells make electron gain, loss and sharing energetically unfavourable under ordinary conditions.
Q33. Match the element symbols with their classes: A. Sm; B. Cs; C. Os; D. Np. Classes: 1. Transition; 2. Alkali; 3. Actinoid; 4. Lanthanoid.
[UPSC CDS-I General Knowledge, 12 April 2026]
(A) A-4, B-2, C-1, D-3
(B) A-4, B-1, C-2, D-3
(C) A-3, B-1, C-2, D-4
(D) A-3, B-2, C-1, D-4
Answer: (A) A-4, B-2, C-1, D-3
Explanation: Samarium is a lanthanoid, caesium an alkali metal, osmium a transition metal and neptunium an actinoid. These classifications follow their electronic structures and periodic-table blocks. Thus the matching sequence is A-4, B-2, C-1 and D-3.
Q32. Which of the following elements is not classified as a metal?
[RRB NTPC Graduate CBT-I, 27 March 2026, Shift 3]
(A) Sulfur
(B) Potassium
(C) Calcium
(D) Sodium
Answer: (A) Sulfur
Explanation: Sulfur is a Group 16 non-metal, generally brittle and a poor conductor of electricity. Potassium and sodium are Group 1 alkali metals, while calcium belongs to Group 2. All three metallic options typically form positively charged ions.
Q31. Which gas in the options does not belong to the noble-gas family?
[RRB NTPC Graduate CBT-I, 19 March 2026, Shift 1]
(A) Helium
(B) Oxygen
(C) Argon
(D) Neon
Answer: (B) Oxygen
Explanation: Oxygen is in Group 16 and has six valence electrons, making it chemically reactive. Helium, argon and neon are Group 18 noble gases, characterized by complete outer shells and very low chemical reactivity under normal conditions.
Q30. Who defined an element as a substance that cannot be broken down by ordinary chemical reactions?
[RRB Group D, 21 December 2025, Shift 3]
(A) Antoine Laurent Lavoisier
(B) Robert Hooke
(C) Robert Boyle
(D) Charles Darwin
Answer: (A) Antoine Laurent Lavoisier
Explanation: Antoine Lavoisier used an operational definition of an element: a substance that contemporary chemical methods could not decompose into simpler substances. His 1789 chemistry treatise helped modernize the classification of substances and established more systematic chemical terminology.
Q29. Arrange these elements by increasing quantity in a typical 70-kg human body: 1. Sodium; 2. Potassium; 3. Copper; 4. Iron.
[UPPSC PCS Preliminary GS-I, 12 October 2025]
(A) 4, 3, 2, 1
(B) 3, 4, 1, 2
(C) 3, 4, 2, 1
(D) 4, 3, 1, 2
Answer: (B) 3, 4, 1, 2
Explanation: Copper occurs only in trace quantities in the human body, followed by iron at a few grams. Sodium and potassium are present in substantially larger amounts, with potassium generally exceeding sodium. The increasing sequence is copper, iron, sodium, potassium.
Q28. Place these major crustal elements in increasing order of mass percentage: 1. Aluminium; 2. Calcium; 3. Silicon; 4. Oxygen.
[UPSC CDS-II General Knowledge, 14 September 2025]
(A) 3, 4, 1, 2
(B) 4, 3, 1, 2
(C) 2, 1, 3, 4
(D) 1, 2, 3, 4
Answer: (C) 2, 1, 3, 4
Explanation: The approximate mass percentages in Earth’s crust are calcium 3.6%, aluminium 8.1%, silicon 27.7% and oxygen 46.6%. Therefore, the ascending sequence is calcium, aluminium, silicon and oxygen, corresponding to the code 2, 1, 3, 4.
Q27. Which electronic configuration represents transition-metal elements most generally?
[UPSC CDS-II General Knowledge, 14 September 2025]
(A) (n−2)d¹⁻¹⁰ ns²
(B) (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns²
(C) ns² np⁶ nd¹⁻¹⁰
(D) (n−1)d¹⁻¹⁰ ns⁰⁻²
Answer: (D) (n−1)d¹⁻¹⁰ ns⁰⁻²
Explanation: Transition metals belong to the d-block, where electrons occupy the penultimate d subshell. Their general electronic configurations involve (n−1)d orbitals and outer ns orbitals, with exceptions caused by orbital-energy similarities. This accounts for variable oxidation states and coloured ions.
Q26. Which formula below is not a typical constituent of Portland cement?
[UPSC NDA-II General Ability Test, 14 September 2025]
(A) 2CaO·SiO₂
(B) 3CaO·SiO₂
(C) 4CaO·SiO₂
(D) 3CaO·Al₂O₃
Answer: (C) 4CaO·SiO₂
Explanation: Portland cement contains dicalcium silicate, tricalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite among its major clinker phases. The formula 4CaO·SiO₂ is not a standard cement clinker compound. Silicates principally contribute to the development of cement strength.
Q25. Why is an alloy classified as a mixture, despite being difficult to separate by simple physical methods?
[RRB NTPC Undergraduate CBT-I, 13 August 2025, Shift 3]
(A) It consists solely of non-metals
(B) Its composition can vary and it retains constituent-related properties
(C) It contains a single gaseous element
(D) All alloys have a fixed composition and are magnetic
Answer: (B) Its composition can vary and it retains constituent-related properties
Explanation: Alloys are mixtures of elements, ordinarily including at least one metal. Their constituent proportions may vary, unlike compounds with fixed chemical formulas. Intimate mixing at the atomic scale makes simple filtration ineffective, but it does not turn alloys into compounds.
Q24. If hydrofluoric acid is weak, what is the nature of its conjugate base, fluoride ion?
[RRB NTPC Graduate CBT-I, 19 June 2025, Shift 1]
(A) A strong acid
(B) A strong base
(C) A neutral species
(D) A weak base
Answer: (D) A weak base
Explanation: Hydrofluoric acid dissociates only partially in water. Its conjugate base, fluoride ion, can accept a proton and therefore displays basic behaviour. However, fluoride is only a weak base in water, though stronger than conjugate bases of strong acids.
Q23. Which combination gives the correct element, symbol and valency for atomic number 11?
[UPSC CDS-I General Knowledge, 13 April 2025]
(A) Lithium, Li, 1
(B) Magnesium, Mg, 2
(C) Boron, B, 3
(D) Sodium, Na, 1
Answer: (D) Sodium, Na, 1
Explanation: Atomic number 11 corresponds to sodium, represented by Na. Its electronic distribution is 2, 8, 1, so it tends to lose one outer electron, forming Na⁺. Consequently, sodium commonly shows a valency of one in compounds.
Q22. Which one of these substances is a metalloid?
[UPSC CDS-I General Knowledge, 13 April 2025]
(A) Germanium
(B) Coke
(C) Iodine
(D) Sugar
Answer: (A) Germanium
Explanation: Germanium is a metalloid with characteristics intermediate between metals and non-metals. It possesses semiconducting properties useful in electronics. Iodine is a non-metal, coke is predominantly carbon, and sugar is an organic compound rather than an element.
Q21. Which element in the list is considered the earliest discovered?
[UPSC NDA-I General Ability Test, 13 April 2025]
(A) Copper
(B) Gold
(C) Oxygen
(D) Uranium
Answer: (A) Copper
Explanation: Copper was among the earliest metals recognized and worked by humans, with archaeological evidence of its use extending deep into prehistory. Gold was also known in antiquity, whereas oxygen and uranium were identified much later through scientific investigation.
Q20. Which chemical formula denotes sulphur hexafluoride?
[SSC MTS, 23 October 2024, Shift 3]
(A) S₂F₆
(B) SF₆
(C) SF₂
(D) S₆F
Answer: (B) SF₆
Explanation: The prefix hexa- indicates six fluorine atoms, and the unprefixed sulfur name indicates one sulfur atom. Sulfur hexafluoride therefore has formula SF₆. It is a stable inorganic gas used for electrical insulation, although it is also a potent greenhouse gas.
Q19. Which inorganic compound is converted into urea through the classic Wöhler rearrangement?
[SSC MTS, 18 October 2024, Shift 1]
(A) Ammonium cyanate
(B) Ammonium phosphate
(C) Ammonium acetate
(D) Ammonium nitrate
Answer: (A) Ammonium cyanate
Explanation: Ammonium cyanate rearranges to form urea, as demonstrated by Friedrich Wöhler in 1828. The experiment proved that an organic compound could be synthesized from inorganic starting material. It became an important challenge to the former vital-force theory.
Q18. Why do these reactions produce copper: Zn + CuSO₄ → ZnSO₄ + Cu; Pb + CuCl₂ → PbCl₂ + Cu?
[SSC MTS, 8 October 2024, Shift 1]
(A) Zinc and lead are unstable as elements
(B) Pressure decomposes copper compounds
(C) Zinc and lead are more reactive than copper
(D) Copper is more reactive than zinc and lead
Answer: (C) Zinc and lead are more reactive than copper
Explanation: Both zinc and lead occur above copper in the metal reactivity series. Each can displace copper ions from suitable compounds, producing elemental copper while forming its own salt. These are single-displacement redox reactions involving electron transfer.
Q17. Which gas is released when iron reacts with steam?
[SSC CGL Tier-I, 24 September 2024, Shift 2]
(A) Hydrogen
(B) Oxygen
(C) Ammonia
(D) Methane
Answer: (A) Hydrogen
Explanation: Hot iron reacts with steam to produce magnetite, Fe₃O₄, and hydrogen gas. The balanced equation is 3Fe + 4H₂O → Fe₃O₄ + 4H₂. Ordinary cold water does not react with iron in the same rapid manner.
Q16. In discussions of periodic trends, what property is usually measured in picometres?
[SSC CGL Tier-I, 18 September 2024, Shift 1]
(A) Atomic radius
(B) Molar mass
(C) Atomic density
(D) Spin quantum number
Answer: (A) Atomic radius
Explanation: A picometre is one trillionth of a metre and is convenient for expressing atomic dimensions. Atomic radii are commonly on the order of tens or hundreds of picometres. Molar mass and spin quantum number require entirely different units or conventions.
Q15. Select the correct formula of magnesium hydroxide.
[SSC CGL Tier-I, 13 September 2024, Shift 2]
(A) MgOH
(B) MgO₂
(C) Mg₂H₂
(D) Mg(OH)₂
Answer: (D) Mg(OH)₂
Explanation: Magnesium forms Mg²⁺ ions, while each hydroxide ion carries a negative charge of one. Two hydroxide ions are therefore required for electrical neutrality. The resulting formula is Mg(OH)₂, a sparingly soluble base used in antacid preparations.
Q14. Which gas produces a characteristic reddish-orange glow in an electric discharge tube?
[SSC CGL Tier-I, 12 September 2024, Shift 2]
(A) Neon
(B) Hydrogen
(C) Argon
(D) Helium
Answer: (A) Neon
Explanation: Neon produces a distinctive reddish-orange glow when electricity excites its atoms. As excited electrons return to lower energy levels, they emit characteristic wavelengths of light. This property made neon popular in illuminated signs and discharge lamps.
Q13. In the thermit process for joining railway tracks, which material acts as the reducing agent?
[WBCS Executive Preliminary, 16 December 2023]
(A) Iron oxide
(B) Aluminium metal
(C) Aluminium oxide
(D) Iron metal
Answer: (B) Aluminium metal
Explanation: Aluminium has a strong affinity for oxygen and reduces iron(III) oxide to molten iron. The thermit reaction liberates considerable heat: Fe₂O₃ + 2Al → 2Fe + Al₂O₃. The molten iron can be used to weld railway rails.
Q12. Chaoite, buckminsterfullerene and graphene are forms of which element?
[SSC MTS, 11 September 2023, Shift 2]
(A) Arsenic
(B) Carbon
(C) Sulphur
(D) Bromine
Answer: (B) Carbon
Explanation: All three are forms, or allotropes, of carbon. Graphene forms a single layer of hexagonally arranged carbon atoms, while buckminsterfullerene has a cage-like molecular structure. Chaoite is a less-common reported carbon form associated with unusual conditions.
Q11. Which element, atomic number 35, is a reddish-brown liquid with an irritating odour?
[SSC MTS, 6 September 2023, Shift 1]
(A) Tennessine
(B) Chlorine
(C) Astatine
(D) Bromine
Answer: (D) Bromine
Explanation: Bromine, symbol Br, is the halogen with atomic number 35. It is a reddish-brown liquid at ordinary room temperature and releases irritating vapours. Unlike bromine, chlorine is gaseous at room temperature, while astatine and tennessine are different halogens.
Q10. For green hydrogen, consider:
(1) combustion-engine fuel,
(2) blending with natural gas,
(3) use in vehicle fuel cells.
How many are feasible?
[UPSC Civil Services Preliminary GS-I, 28 May 2023]
(A) Only one
(B) Only two
(C) All three
(D) None
Answer: (C) All three
Explanation: Green hydrogen is hydrogen made using renewable-powered processes, commonly water electrolysis. It can fuel suitably designed combustion engines, be blended with natural gas within applicable limits, and generate electricity in hydrogen fuel cells for vehicles. Therefore, all three uses are feasible.
Q9. Which alloy listed below primarily consists of copper and zinc?
[SSC CHSL Tier-I 2022 cycle, held 13 March 2023, Shift 3]
(A) Monel metal
(B) Magnalium
(C) Rolled gold
(D) Dutch metal
Answer: (D) Dutch metal
Explanation: Dutch metal, also called composition gold, is a copper-zinc alloy used for gold-coloured decorative leaf. Despite its name, it generally contains no gold. Monel is mainly nickel-copper, and magnalium is principally aluminium-magnesium.
Q8. Which reaction correctly describes manufacture of bleaching powder?
[RRB Group D, 18 September 2022, Shift 1]
(A) NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
(B) Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
(C) NaHCO₃ + H⁺ → CO₂ + H₂O + sodium salt
(D) 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
Answer: (B) Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
Explanation: Bleaching powder is conventionally manufactured by passing chlorine over dry slaked lime, calcium hydroxide. The school-level equation is Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. Its bleaching and disinfecting action is associated with available chlorine and oxidation.
Q7. Which chemical symbol represents a noble gas?
[RRB NTPC CBT-II Level 5, 15 June 2022, Shift 3]
(A) Ca
(B) F
(C) N
(D) Ne
Answer: (D) Ne
Explanation: Ne denotes neon, a Group 18 noble gas with a filled outer electron shell. Ca is calcium, an alkaline-earth metal; F represents fluorine, a halogen; and N represents nitrogen, a Group 15 non-metal. Thus only neon qualifies.
Q6. Which mineral and mining locality are correctly paired?
[RPSC RAS Preliminary, 27 October 2021]
(A) Manganese – Bailadila
(B) Bauxite – Lohardaga
(C) Iron – Koderma
(D) Mica – Talcher
Answer: (B) Bauxite – Lohardaga
Explanation: Lohardaga in Jharkhand is known for bauxite, the principal ore of aluminium. Bailadila is primarily noted for iron ore, Koderma for mica, and Talcher for coal. This makes bauxite–Lohardaga the correctly matched pair.
Q5. Which element accounts for the highest percentage of mass in the human body?
[MPPSC General Studies 2019 Official Paper]
(A) Hydrogen
(B) Nitrogen
(C) Carbon
(D) Oxygen
Answer: (D) Oxygen
Explanation: Oxygen is the most abundant element in the human body by mass, largely because water and many biological molecules contain oxygen. It contributes roughly 65% of body mass, exceeding carbon and hydrogen. By number of atoms, hydrogen is especially abundant.
Q4. Evaluate these material–chemical pairs:
(1) lipstick–lead,
(2) soft drinks–brominated vegetable oils,
(3) Chinese fast food–monosodium glutamate.
Which match?
[UPSC Civil Services Preliminary GS-I, 2017]
(A) 1 only
(B) 2 and 3 only
(C) 1 and 3 only
(D) 1, 2 and 3
Answer: (D) 1, 2 and 3
Explanation: Lead contamination in some lipsticks, brominated vegetable oils historically used in certain soft drinks, and monosodium glutamate used as a flavour enhancer in some Chinese-style fast foods have all raised chemical-use discussions. The examination regarded all three pairs as correctly matched.
Q3. Which examples demonstrate corrosion: blackening of silver, greening of copper, or browning of iron?
[CGPSC Preliminary General Studies 2016 Official Paper]
(A) Black coating on silver
(B) Green coating on copper
(C) Brown coating on iron
(D) All three
(E) None of these
Answer: (D) All three
Explanation: Silver can develop black silver sulfide tarnish; copper commonly develops a green patina; and iron forms reddish-brown rust under suitable conditions. Each is an example of a metal undergoing chemical deterioration through reactions with its surroundings.
Q2. Which substance reacts with glass and therefore should not normally be stored in glass containers?
[WBCS Preliminary 2015 Official Paper]
(A) HNO₃
(B) HCl
(C) HF
(D) HBr
Answer: (C) HF
Explanation: Hydrofluoric acid attacks silica, a major constituent of glass, by forming silicon-fluoride species. Consequently, HF is commonly handled in compatible plastic containers rather than glass vessels. The other listed mineral acids do not characteristically etch ordinary glass in this way.
Q1. What is the molecular geometry of sulphur hexafluoride (SF₆)?
[45th BPSC Preliminary Examination, 2002]
(A) Trigonal pyramidal
(B) Octahedral
(C) Planar
(D) Tetrahedral
Answer: (B) Octahedral
Explanation: Sulphur hexafluoride has six fluorine atoms bonded to a central sulphur atom. The six bonding directions arrange symmetrically toward the corners of an octahedron, with approximate F–S–F bond angles of 90 degrees. Therefore, SF₆ has octahedral molecular geometry.