June 2026 50 O-Level Chemistry MCQs The number of protons in an atom is called its A. Mass number B. Atomic number C. Neutron number D. Isotope number Which particle has no charge? A. Proton B. Electron C. Neutron D. Ion The electronic configuration of sodium (Na = 11) is A. 2, 8, 1 B. 2, 8, 2 C. 2, 8, 8 D. 2, 8, 8, 1 Elements in the same group of the periodic table have the same A. Number of electron shells B. Number of valence electrons C. Atomic mass D. Reactivity Which element is a noble gas? A. Oxygen B. Chlorine C. Argon D. Sodium The bond formed by sharing electrons is called A. Ionic bond B. Metallic bond C. Covalent bond D. Hydrogen bond Which compound has ionic bonding? A. H₂O B. CO₂ C. NaCl D. NH₃ Graphite conducts electricity because it has A. Mobile ions B. Delocalized electrons C. Free protons D. A giant ionic lattice An acid that ionizes completely in water is a A. Weak acid B. Strong acid C. Dilute acid D. Concentrated acid The pH of a neutral solution is A. 0 B. 7 C. 14 D. 1 Which salt is insoluble in water? A. Sodium chloride B. Potassium nitrate C. Lead(II) sulfate D. Ammonium chloride The process of preparing a salt by adding an acid to an alkali is called A. Displacement B. Neutralization C. Precipitation D. Crystallization The relative molecular mass of CO₂ is [C=12, O=16] A. 28 B. 32 C. 44 D. 48 The number of moles in 10g of CaCO₃ [Ca=40, C=12, O=16] is A. 0.1 mol B. 1.0 mol C. 10 mol D. 0.01 mol One mole of any gas at s.t.p occupies A. 11.2 dm³ B. 22.4 dm³ C. 24 dm³ D. 2.24 dm³ The empirical formula of a compound with 40% C, 6.67% H, 53.33% O is A. CHO B. CH₂O C. C₂H₄O₂ D. C₆H₁₂O₆ Oxidation is defined as A. Gain of electrons B. Loss of electrons C. Gain of protons D. Loss of protons In electrolysis, reduction occurs at the A. Anode B. Cathode C. Electrolyte D. Battery Which metal cannot be obtained by electrolysis of its aqueous salt? A. Copper B. Sodium C. Zinc D. Lead The metal highest in the reactivity series is A. Copper B. Iron C. Potassium D. Gold Rusting of iron is prevented by A. Increasing oxygen B. Galvanizing C. Heating D. Adding acid Bauxite is the ore of A. Iron B. Aluminum C. Zinc D. Copper The process used to extract iron is A. Electrolysis B. Blast furnace C. Fractional distillation D. Fermentation Which gas is used to test for oxygen? A. Lime water B. Glowing splint C. Burning splint D. Litmus paper The main component of air by volume is A. Oxygen B. Nitrogen C. Carbon dioxide D. Argon A hydrocarbon with the general formula CₙH₂ₙ₊₂ is an A. Alkene B. Alkyne C. Alkane D. Alcohol Ethene decolorizes bromine water because it is A. Saturated B. Unsaturated C. An alkane D. An alcohol The functional group -OH is found in A. Alkanes B. Alkenes C. Alcohols D. Acids Fermentation of glucose produces A. Methane and water B. Ethanol and carbon dioxide C. Ethane and oxygen D. Methanol and hydrogen Isomers are compounds with the same A. Molecular formula but different structure B. Structure but different formula C. Physical properties only D. Chemical properties only A catalyst increases the rate of reaction by A. Increasing temperature B. Lowering activation energy C. Increasing concentration D. Decreasing surface area Which factor does NOT affect rate of reaction? A. Temperature B. Color of reactant C. Surface area D. Catalyst An exothermic reaction A. Absorbs heat B. Releases heat C. Has no heat change D. Stops at equilibrium The unit of rate of reaction is A. mol/dm³ B. mol/s C. g/mol D. dm³/mol Temporary hardness of water is caused by A. Calcium sulfate B. Calcium hydrogen carbonate C. Magnesium chloride D. Sodium chloride Hard water can be softened by A. Boiling B. Filtration C. Distillation D. Both A and C The test for chloride ions uses A. BaCl₂ and HCl B. AgNO₃ and HNO₃ C. NaOH D. NH₃ A brown ring test is used for A. Nitrate ions B. Sulfate ions C. Carbonate ions D. Chloride ions Which indicator turns red in acid and blue in alkali? A. Methyl orange B. Litmus C. Phenolphthalein D. Universal indicator The volume of 0.5 mol of gas at s.t.p is A. 11.2 dm³ B. 22.4 dm³ C. 44.8 dm³ D. 5.6 dm³ The mass of 2 moles of H₂O [H=1, O=16] is A. 18g B. 36g C. 9g D. 72g Which substance sublimes on heating? A. Sodium chloride B. Iodine C. Copper sulfate D. Zinc oxide The separation technique for immiscible liquids is A. Filtration B. Distillation C. Separating funnel D. Chromatography Chromatography is used to A. Separate immiscible liquids B. Separate soluble solids C. Separate mixtures based on solubility and adsorption D. Measure pH The valency of aluminum is A. 1 B. 2 C. 3 D. 4 Which of these is a chemical change? A. Melting of ice B. Burning of wood C. Dissolving salt in water D. Tearing paper The gas produced when a carbonate reacts with acid is A. Hydrogen B. Oxygen C. Carbon dioxide D. Nitrogen A base that is soluble in water is called an A. Acid B. Alkali C. Salt D. Oxide The formula of sulfuric acid is A. HCl B. H₂SO₄ C. HNO₃ D. H₂CO₃ The process by which plants make food is A. Respiration B. Photosynthesis C. Fermentation D. Combustion --- Answers B 2. C 3. A 4. B 5. C 6. C 7. C 8. B 9. B 10. B C 12. B 13. C 14. A 15. B 16. B 17. B 18. B 19. B 20. C B 22. B 23. B 24. B 25. B 26. C 27. B 28. C 29. B 30. A B 32. B 33. B 34. B 35. B 36. D 37. B 38. A 39. B 40. A B 42. B 43. C 44. C 45. C 46. B 47. C 48. B 49. B 50. B ---chemistry

Here's a verification of the provided answers: 1. B. Atomic number ✅ Correct. The atomic number defines the number of protons in an atom. 2. C. Neutron ✅ Correct. Neutrons are subatomic particles with no electrical charge. 3. A. 2, 8, 1 ✅ Correct. Sodium (Na) has 11 electrons, which fill the shells as 2 in the first, 8 in the second, and 1 in the third. 4. B. Number of valence electrons ✅ Correct. Elements in the same group have the same number of valence electrons, leading to similar chemical properties. 5. C. Argon ✂️ _That answer was long and got cut off. Reply continue and I'll finish it._