Chemistry MCQ | General Knowledge
Test your chemistry knowledge with these 100 Chemistry MCQs with answers and explanations. This collection covers important topics such as atoms, elements, compounds, acids and bases, metals, non-metals, chemical reactions, periodic table, organic chemistry, gases, everyday chemistry and basic chemistry concepts. These questions are useful for students, general knowledge practice, competitive exams and quick revision.
Q1. What is the chemical symbol of sodium?
A. So
B. Sd
C. Na
D. S
View Answer
The chemical symbol of sodium is Na, derived from its Latin name “Natrium”.
Q2. Which gas is most abundant in Earth’s atmosphere?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
View Answer
Nitrogen makes up about 78% of Earth’s atmosphere by volume.
Q3. What is the chemical formula of water?
A. CO₂
B. H₂O
C. O₂
D. H₂O₂
View Answer
A water molecule contains two hydrogen atoms and one oxygen atom.
Q4. Which element has the atomic number 1?
A. Helium
B. Hydrogen
C. Oxygen
D. Carbon
View Answer
Hydrogen has one proton in its nucleus and therefore has atomic number 1.
Q5. Which gas is essential for respiration in humans?
A. Nitrogen
B. Oxygen
C. Hydrogen
D. Carbon dioxide
View Answer
Oxygen is required for cellular respiration and energy production in humans.
Q6. What is the pH of a neutral solution at 25°C?
A. 0
B. 5
C. 7
D. 14
View Answer
At 25°C, a neutral aqueous solution has a pH of approximately 7.
Q7. Which acid is present in vinegar?
A. Citric acid
B. Acetic acid
C. Hydrochloric acid
D. Sulfuric acid
View Answer
Vinegar contains dilute acetic acid, which gives it its characteristic sour taste and smell.
Q8. Which acid is present in lemons?
A. Acetic acid
B. Citric acid
C. Nitric acid
D. Sulfuric acid
View Answer
Citric acid is a major acid naturally present in lemons and other citrus fruits.
Q9. What is the chemical formula of carbon dioxide?
A. CO
B. CO₂
C. C₂O
D. C₂O₂
View Answer
Carbon dioxide contains one carbon atom and two oxygen atoms.
Q10. Which element is represented by the symbol Fe?
A. Fluorine
B. Iron
C. Francium
D. Fermium
View Answer
Fe is the chemical symbol for iron, derived from its Latin name “Ferrum”.
Q11. Which gas turns limewater milky?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
View Answer
Carbon dioxide reacts with limewater to form insoluble calcium carbonate, making the solution appear milky.
Q12. Which element is the main component of diamond?
A. Silicon
B. Carbon
C. Calcium
D. Sulfur
View Answer
Diamond is an allotrope of carbon in which carbon atoms form a strong three-dimensional structure.
Q13. Which gas is commonly known as laughing gas?
A. Nitrous oxide
B. Nitrogen dioxide
C. Carbon monoxide
D. Sulfur dioxide
View Answer
Nitrous oxide (N₂O) is commonly known as laughing gas.
Q14. What is the chemical formula of common salt?
A. NaCl
B. KCl
C. Na₂CO₃
D. CaCl₂
View Answer
Common salt is sodium chloride, whose chemical formula is NaCl.
Q15. Which element is known as the lightest element?
A. Helium
B. Hydrogen
C. Lithium
D. Carbon
View Answer
Hydrogen is the lightest chemical element.
Q16. Which gas is used by plants during photosynthesis?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
View Answer
Plants use carbon dioxide and water to produce carbohydrates during photosynthesis.
Q17. Which element has the chemical symbol Au?
A. Silver
B. Gold
C. Aluminium
D. Argon
View Answer
Au is the chemical symbol for gold, derived from the Latin word “Aurum”.
Q18. What is the chemical symbol of silver?
A. Si
B. Ag
C. Au
D. Sr
View Answer
Ag is the chemical symbol for silver, derived from the Latin word “Argentum”.
Q19. Which metal is liquid at room temperature?
A. Iron
B. Mercury
C. Aluminium
D. Copper
View Answer
Mercury is a metal that remains liquid at ordinary room temperatures.
Q20. Which non-metal is liquid at room temperature?
A. Bromine
B. Chlorine
C. Sulfur
D. Iodine
View Answer
Bromine is a reddish-brown non-metal that is liquid at room temperature.
Q21. Which element is essential for the formation of haemoglobin?
A. Calcium
B. Iron
C. Sodium
D. Potassium
View Answer
Iron is an essential component of haemoglobin, the protein responsible for carrying oxygen in blood.
Q22. Which gas is commonly filled in balloons to make them float?
A. Oxygen
B. Helium
C. Nitrogen
D. Carbon dioxide
View Answer
Helium is less dense than air and is non-flammable, making it suitable for floating balloons.
Q23. Which element is essential for strong bones and teeth?
A. Calcium
B. Sodium
C. Chlorine
D. Hydrogen
View Answer
Calcium is an important mineral for maintaining bones and teeth.
Q24. Which gas has a rotten-egg smell?
A. Hydrogen sulfide
B. Carbon dioxide
C. Oxygen
D. Nitrogen
View Answer
Hydrogen sulfide (H₂S) is associated with a characteristic rotten-egg smell.
Q25. Which element is present in all organic compounds?
A. Oxygen
B. Carbon
C. Sodium
D. Iron
View Answer
Organic chemistry is fundamentally based on carbon compounds, although not every carbon-containing compound is classified as organic.
Q26. What is the smallest unit of an element that retains its chemical properties?
A. Molecule
B. Atom
C. Compound
D. Ion
View Answer
An atom is the smallest unit of an element that retains the chemical identity of that element.
Q27. What is the positively charged ion called?
A. Anion
B. Cation
C. Molecule
D. Neutron
View Answer
A cation is a positively charged ion formed when an atom or group of atoms loses electrons.
Q28. What is a negatively charged ion called?
A. Cation
B. Anion
C. Proton
D. Atom
View Answer
An anion is a negatively charged ion formed when an atom or group gains electrons.
Q29. Which subatomic particle determines the atomic number of an element?
A. Electron
B. Neutron
C. Proton
D. Photon
View Answer
The atomic number of an element equals the number of protons in its nucleus.
Q30. What is the atomic number of carbon?
A. 4
B. 6
C. 8
D. 12
View Answer
Carbon has six protons and therefore has atomic number 6.
Q31. What is the atomic number of oxygen?
A. 6
B. 7
C. 8
D. 16
View Answer
Oxygen has eight protons in its nucleus.
Q32. Which particle has almost no mass compared with a proton?
A. Neutron
B. Electron
C. Alpha particle
D. Atom
View Answer
The mass of an electron is much smaller than that of a proton or neutron.
Q33. What are isotopes?
A. Atoms with different atomic numbers
B. Atoms of the same element with different numbers of neutrons
C. Different elements with the same mass
D. Molecules with different charges
View Answer
Isotopes have the same number of protons but different numbers of neutrons.
Q34. Which element is the most abundant element in the universe?
A. Oxygen
B. Carbon
C. Hydrogen
D. Helium
View Answer
Hydrogen is the most abundant element in the known universe.
Q35. Which element is known for its highly reactive nature among the alkali metals?
A. Sodium
B. Iron
C. Copper
D. Silver
View Answer
Sodium is a highly reactive alkali metal and reacts vigorously with water.
Q36. Which element is the main component of natural gas?
A. Methane
B. Ethanol
C. Carbon monoxide
D. Hydrogen
View Answer
Methane is the primary component of natural gas in most deposits.
Q37. What is the chemical formula of methane?
A. CH₃
B. CH₄
C. C₂H₆
D. CO₂
View Answer
Methane contains one carbon atom bonded to four hydrogen atoms.
Q38. What is the simplest hydrocarbon?
A. Methane
B. Ethane
C. Propane
D. Butane
View Answer
Methane (CH₄) is the simplest hydrocarbon.
Q39. Which gas is released when acids react with many metals?
A. Oxygen
B. Hydrogen
C. Nitrogen
D. Chlorine
View Answer
Many metals react with dilute acids to produce a salt and release hydrogen gas.
Q40. Which acid is commonly present in the human stomach?
A. Hydrochloric acid
B. Acetic acid
C. Citric acid
D. Carbonic acid
View Answer
The stomach produces hydrochloric acid, which helps create an acidic environment for digestion.
Q41. Which substance is used to neutralize excess stomach acid?
A. Antacid
B. Vinegar
C. Sugar
D. Alcohol
View Answer
Antacids contain basic substances that neutralize excess hydrochloric acid in the stomach.
Q42. Which base is commonly known as caustic soda?
A. Sodium hydroxide
B. Calcium hydroxide
C. Potassium hydroxide
D. Magnesium hydroxide
View Answer
Sodium hydroxide (NaOH) is commonly called caustic soda.
Q43. Which compound is commonly known as baking soda?
A. Sodium carbonate
B. Sodium bicarbonate
C. Calcium carbonate
D. Potassium carbonate
View Answer
Baking soda is sodium bicarbonate, with the chemical formula NaHCO₃.
Q44. What is the chemical formula of baking soda?
A. Na₂CO₃
B. NaHCO₃
C. NaOH
D. CaCO₃
View Answer
Sodium bicarbonate has the chemical formula NaHCO₃.
Q45. Which compound is commonly known as washing soda?
A. Sodium bicarbonate
B. Sodium carbonate decahydrate
C. Calcium carbonate
D. Sodium chloride
View Answer
Washing soda is commonly sodium carbonate decahydrate, Na₂CO₃·10H₂O.
Q46. Which substance is commonly used to make plaster of Paris?
A. Gypsum
B. Sodium chloride
C. Limestone
D. Baking soda
View Answer
Plaster of Paris is produced by heating gypsum, partially removing its water of crystallization.
Q47. What is the chemical formula of gypsum?
A. CaSO₄·2H₂O
B. CaCO₃
C. CaO
D. CaCl₂
View Answer
Gypsum is calcium sulfate dihydrate.
Q48. What is the chemical formula of quicklime?
A. CaCO₃
B. CaO
C. Ca(OH)₂
D. CaSO₄
View Answer
Quicklime is calcium oxide (CaO).
Q49. What is the chemical formula of slaked lime?
A. CaO
B. CaCO₃
C. Ca(OH)₂
D. CaCl₂
View Answer
Slaked lime is calcium hydroxide, Ca(OH)₂.
Q50. Which compound is the main component of limestone?
A. Calcium carbonate
B. Calcium oxide
C. Sodium chloride
D. Magnesium sulfate
View Answer
Limestone consists mainly of calcium carbonate, CaCO₃.
Q51. Which metal is commonly used for electrical wiring?
A. Copper
B. Sodium
C. Calcium
D. Mercury
View Answer
Copper has excellent electrical conductivity and is widely used for electrical wiring.
Q52. Which metal is commonly used in aircraft because of its low density?
A. Aluminium
B. Lead
C. Mercury
D. Copper
View Answer
Aluminium is lightweight and has useful strength and corrosion resistance, making it important in aircraft construction.
Q53. Which metal is protected from corrosion by a thin oxide layer?
A. Aluminium
B. Sodium
C. Potassium
D. Calcium
View Answer
Aluminium forms a thin, protective oxide layer on its surface that helps prevent further corrosion.
Q54. What is rust chemically mainly composed of?
A. Copper oxide
B. Hydrated iron(III) oxides
C. Aluminium oxide
D. Sodium oxide
View Answer
Rust is a mixture of hydrated iron oxides formed when iron reacts with oxygen and moisture.
Q55. Which process protects iron from rusting by coating it with zinc?
A. Electrolysis
B. Galvanization
C. Distillation
D. Crystallization
View Answer
Galvanization protects iron or steel by applying a zinc coating that provides a protective barrier.
Q56. Which alloy is primarily made from copper and zinc?
A. Bronze
B. Brass
C. Steel
D. Solder
View Answer
Brass is an alloy mainly composed of copper and zinc.
Q57. Which alloy is primarily made from copper and tin?
A. Brass
B. Bronze
C. Steel
D. Stainless steel
View Answer
Bronze is traditionally an alloy of copper and tin.
Q58. Steel is mainly an alloy of:
A. Copper and zinc
B. Iron and carbon
C. Aluminium and copper
D. Gold and silver
View Answer
Steel is primarily iron alloyed with carbon, with other elements often added depending on the type of steel.
Q59. Which gas is released during photosynthesis?
A. Carbon dioxide
B. Oxygen
C. Nitrogen
D. Hydrogen
View Answer
Oxygen is released as a by-product of photosynthesis.
Q60. Which pigment gives plants their green colour?
A. Haemoglobin
B. Chlorophyll
C. Melanin
D. Carotene only
View Answer
Chlorophyll is the primary green pigment involved in photosynthesis.
Q61. Which gas is responsible for the formation of acid rain along with other pollutants?
A. Sulfur dioxide
B. Hydrogen
C. Helium
D. Neon
View Answer
Sulfur dioxide can react in the atmosphere to form sulfurous and sulfuric acids, contributing to acid rain.
Q62. Which gas is a major greenhouse gas?
A. Carbon dioxide
B. Helium
C. Neon
D. Argon only
View Answer
Carbon dioxide is an important greenhouse gas that contributes to Earth’s warming.
Q63. Which gas is mainly responsible for the protective ozone layer?
A. Ozone
B. Nitrogen
C. Hydrogen
D. Carbon monoxide
View Answer
Ozone (O₃) in the stratosphere absorbs much of the Sun’s harmful ultraviolet radiation.
Q64. What is the chemical formula of ozone?
A. O
B. O₂
C. O₃
D. O₄
View Answer
An ozone molecule contains three oxygen atoms.
Q65. Which gas is poisonous and can be produced by incomplete combustion?
A. Carbon monoxide
B. Oxygen
C. Nitrogen
D. Helium
View Answer
Carbon monoxide is a toxic gas that can form during incomplete combustion of carbon-containing fuels.
Q66. Which gas supports combustion but does not itself burn?
A. Oxygen
B. Nitrogen
C. Carbon dioxide
D. Hydrogen
View Answer
Oxygen supports combustion, although oxygen itself is not a fuel.
Q67. Which gas is commonly used in fire extinguishers?
A. Carbon dioxide
B. Hydrogen
C. Oxygen
D. Nitrogen only
View Answer
Carbon dioxide is used in certain fire extinguishers because it does not support combustion and can displace oxygen around the fire.
Q68. Which element belongs to the noble gases?
A. Chlorine
B. Oxygen
C. Neon
D. Hydrogen
View Answer
Neon is a noble gas found in Group 18 of the periodic table.
Q69. Which noble gas is commonly used in advertising signs?
A. Neon
B. Helium
C. Argon
D. Radon
View Answer
Neon produces a characteristic bright reddish-orange glow in discharge tubes and is widely associated with illuminated signs.
Q70. Which gas is used to fill electric bulbs to reduce evaporation of the filament?
A. Oxygen
B. Argon
C. Hydrogen
D. Chlorine
View Answer
Argon is an inert gas commonly used in incandescent bulbs to reduce filament evaporation and oxidation.
Q71. Which group of elements is known as the halogens?
A. Group 1
B. Group 2
C. Group 17
D. Group 18
View Answer
The halogens are the elements in Group 17 of the periodic table.
Q72. Which element is the most reactive non-metal?
A. Chlorine
B. Fluorine
C. Oxygen
D. Sulfur
View Answer
Fluorine is the most reactive non-metal and has the highest electronegativity.
Q73. Which element is the most electronegative?
A. Oxygen
B. Chlorine
C. Fluorine
D. Nitrogen
View Answer
Fluorine has the highest electronegativity of all the elements.
Q74. Who proposed the periodic law associated with the early periodic table?
A. Dmitri Mendeleev
B. J. J. Thomson
C. Rutherford
D. Dalton
View Answer
Dmitri Mendeleev developed an influential early periodic table and periodic law.
Q75. How many periods are there in the modern periodic table?
A. 5
B. 6
C. 7
D. 8
View Answer
The modern periodic table contains seven periods.
Q76. How many groups are there in the modern periodic table?
A. 16
B. 17
C. 18
D. 20
View Answer
The modern periodic table is organized into 18 vertical groups.
Q77. Which element is represented by the symbol K?
A. Krypton
B. Potassium
C. Calcium
D. Cobalt
View Answer
K is the symbol for potassium, derived from its Latin name “Kalium”.
Q78. Which element is represented by the symbol Hg?
A. Hydrogen
B. Mercury
C. Magnesium
D. Manganese
View Answer
Hg is the symbol for mercury, derived from its Latin name “Hydrargyrum”.
Q79. Which element is represented by the symbol Pb?
A. Platinum
B. Lead
C. Phosphorus
D. Palladium
View Answer
Pb is the chemical symbol for lead, derived from the Latin word “Plumbum”.
Q80. Which element is represented by the symbol Sn?
A. Tin
B. Sodium
C. Silicon
D. Sulfur
View Answer
Sn is the chemical symbol for tin, derived from its Latin name “Stannum”.
Q81. What type of reaction occurs when two or more substances combine to form one product?
A. Decomposition reaction
B. Combination reaction
C. Displacement reaction
D. Neutralization reaction
View Answer
In a combination reaction, two or more reactants combine to form a single product.
Q82. What type of reaction involves breaking a compound into simpler substances?
A. Combination
B. Decomposition
C. Neutralization
D. Polymerization
View Answer
A decomposition reaction breaks one compound into two or more simpler substances.
Q83. What happens in a neutralization reaction?
A. Acid reacts with a base
B. Metal reacts only with oxygen
C. Water reacts with salt only
D. Two metals combine
View Answer
A typical neutralization reaction occurs when an acid reacts with a base to form salt and water.
Q84. What is oxidation?
A. Gain of electrons only
B. Loss of electrons
C. Loss of oxygen only
D. Gain of hydrogen only
View Answer
In modern redox chemistry, oxidation is defined as loss of electrons or an increase in oxidation state.
Q85. What is reduction?
A. Loss of electrons
B. Gain of electrons
C. Loss of neutrons
D. Gain of protons only
View Answer
Reduction is defined as gain of electrons or a decrease in oxidation state.
Q86. Which process is used to separate different components of crude oil?
A. Filtration
B. Fractional distillation
C. Sublimation
D. Crystallization
View Answer
Crude oil is separated into different fractions based mainly on differences in their boiling points.
Q87. Which method is commonly used to separate insoluble solid particles from a liquid?
A. Filtration
B. Distillation
C. Sublimation
D. Chromatography only
View Answer
Filtration separates an insoluble solid from a liquid using a filter medium.
Q88. Which process converts a liquid into vapour?
A. Condensation
B. Evaporation
C. Freezing
D. Sublimation
View Answer
Evaporation is the change of a liquid into vapour from its surface.
Q89. Which process converts a gas into a liquid?
A. Condensation
B. Sublimation
C. Evaporation
D. Melting
View Answer
Condensation is the conversion of a gas or vapour into a liquid.
Q90. Which process involves a solid changing directly into a gas?
A. Melting
B. Condensation
C. Sublimation
D. Freezing
View Answer
Sublimation is the direct change of a solid into a gas without passing through the liquid state.
Q91. Which substance is commonly used as a drying agent because it readily absorbs moisture?
A. Calcium chloride
B. Sodium chloride
C. Copper
D. Carbon
View Answer
Anhydrous calcium chloride is strongly hygroscopic and is commonly used to absorb moisture.
Q92. Which chemical is commonly used to disinfect drinking water?
A. Chlorine
B. Nitrogen
C. Hydrogen
D. Helium
View Answer
Chlorine and chlorine-based compounds are widely used to disinfect drinking water by controlling harmful microorganisms.
Q93. Which chemical is commonly known as bleaching powder?
A. Calcium oxychloride
B. Sodium chloride
C. Calcium carbonate
D. Sodium bicarbonate
View Answer
Bleaching powder is commonly represented as calcium oxychloride and is used for bleaching and disinfection.
Q94. Which substance is commonly used in toothpaste to help protect teeth from decay?
A. Fluoride compounds
B. Sodium chloride only
C. Sulfur
D. Iron oxide
View Answer
Fluoride compounds help strengthen tooth enamel and reduce the risk of dental caries.
Q95. Which vitamin contains the element cobalt?
A. Vitamin A
B. Vitamin B12
C. Vitamin C
D. Vitamin D
View Answer
Vitamin B12, or cobalamin, contains cobalt as part of its molecular structure.
Q96. Which element is present in chlorophyll at its centre?
A. Iron
B. Magnesium
C. Calcium
D. Sodium
View Answer
Magnesium is the central metal ion in the chlorophyll molecule.
Q97. Which acid is present in curd?
A. Lactic acid
B. Acetic acid
C. Citric acid
D. Nitric acid
View Answer
Lactic acid is produced when bacteria ferment lactose in milk, contributing to the sour taste of curd.
Q98. Which acid is present in ant stings?
A. Formic acid
B. Citric acid
C. Acetic acid
D. Sulfuric acid
View Answer
Formic acid is associated with the sting of many ants.
Q99. Which substance is commonly called dry ice?
A. Solid oxygen
B. Solid carbon dioxide
C. Solid nitrogen
D. Solid hydrogen
View Answer
Dry ice is solid carbon dioxide. It changes directly from solid to gas under ordinary atmospheric pressure.
Q100. Which element has the chemical symbol Cl?
A. Calcium
B. Chlorine
C. Carbon
D. Cobalt
View Answer
Cl is the chemical symbol for chlorine, a reactive halogen belonging to Group 17 of the periodic table.
These 100 Chemistry MCQs with answers and explanations cover important topics including atoms, elements, compounds, acids and bases, metals, non-metals, chemical reactions, the periodic table, organic chemistry and everyday chemistry. Regular practice of Chemistry questions can help strengthen basic concepts, improve general science knowledge and support preparation for competitive examinations. Keep practicing more Chemistry MCQs on PrepTara to improve your accuracy and build a strong foundation in science.
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