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100 important General Science MCQs on Chemistry, covering key topics commonly asked in UPSC, SSC, and other competitive exams.

General Science - Chemistry (100 Important MCQs)

1. Basic Concepts of Chemistry (1-15)

Which of the following is the smallest particle of an element?

a) Molecule

b) Atom

c) Ion

d) Proton

Ans:

b) Atom

Who discovered the electron?

a) Ernest Rutherford

b) J.J. Thomson

c) Niels Bohr

d) James Chadwick

Ans:

b) J.J. Thomson

Which subatomic particle has no charge?

a) Proton

b) Electron

c) Neutron

d) Positron

Ans:

c) Neutron

The number of protons in the nucleus of an atom is called:

a) Atomic number

b) Mass number

c) Isotope

d) Atomic weight

Ans:

a) Atomic number

Which element has the lowest atomic number?

a) Hydrogen

b) Helium

c) Oxygen

d) Lithium

Ans:

a) Hydrogen

The mass of an atom is concentrated in its:

a) Nucleus

b) Electron cloud

c) Outer shell

d) None of the above

Ans:

a) Nucleus

Which element is a liquid at room temperature?

a) Iron

b) Mercury

c) Lead

d) Sodium

Ans:

b) Mercury

Which gas is known as "laughing gas"?

a) Carbon dioxide

b) Nitrous oxide

c) Oxygen

d) Nitrogen dioxide

Ans:

b) Nitrous oxide

Which gas is the most abundant in Earth’s atmosphere?

a) Oxygen

b) Nitrogen

c) Carbon dioxide

d) Hydrogen

Ans:

b) Nitrogen

What is the chemical symbol for gold?

a) Ag

b) Au

c) Pb

d) Pt

Ans:

b) Au

Which gas is commonly used in balloons?

a) Hydrogen

b) Helium

c) Oxygen

d) Nitrogen

Ans:

b) Helium

Which of the following is an alkaline earth metal?

a) Sodium

b) Potassium

c) Calcium

d) Iron

Ans:

c) Calcium

Who gave the modern periodic table?

a) Mendeleev

b) Lavoisier

c) Dalton

d) Avogadro

Ans:

a) Mendeleev

What is Avogadro’s number?

a) 6.02 × 10²²

b) 6.02 × 10²³

c) 3.01 × 10²³

d) 1.67 × 10²⁴

Ans:

b) 6.02 × 10²³

Which of the following is a noble gas?

a) Oxygen

b) Argon

c) Hydrogen

d) Nitrogen

Ans:

b) Argon

2. Chemical Bonding & Reactions (16-30)

The bond formed by sharing of electrons is called:

a) Ionic bond

b) Covalent bond

c) Hydrogen bond

d) Metallic bond

Ans:

b) Covalent bond

Which of the following is an ionic compound?

a) H₂O

b) NaCl

c) CO₂

d) NH₃

Ans:

b) NaCl

The pH of neutral water is:

a) 0

b) 7

c) 10

d) 14

Ans:

b) 7

Which substance turns blue litmus red?

a) Acid

b) Base

c) Salt

d) Alcohol

Ans:

a) Acid

Which gas is evolved when an acid reacts with a metal?

a) Oxygen

b) Carbon dioxide

c) Hydrogen

d) Nitrogen

Ans:

c) Hydrogen

Which of the following is a strong acid?

a) Acetic acid

b) Hydrochloric acid

c) Citric acid

d) Carbonic acid

Ans:

b) Hydrochloric acid

Which of the following is a base?

a) HCl

b) NaOH

c) H₂SO₄

d) CH₃COOH

Ans:

b) NaOH

Rusting of iron occurs due to:

a) Reaction with CO₂

b) Reaction with O₂ and H₂O

c) Reaction with N₂

d) None of the above

Ans:

b) Reaction with O₂ and H₂O

What is the chemical formula of baking soda?

a) Na₂CO₃

b) NaHCO₃

c) K₂CO₃

d) CaCO₃

Ans:

b) NaHCO₃

Which gas is produced during respiration?

a) Oxygen

b) Carbon dioxide

c) Nitrogen

d) Hydrogen

Ans:

b) Carbon dioxide

3. States of Matter & Solutions (26-50)

Which state of matter has a definite shape and volume?

a) Solid

b) Liquid

c) Gas

d) Plasma

Ans:

a) Solid

Which state of matter has the highest energy?

a) Solid

b) Liquid

c) Gas

d) Plasma

Ans:

d) Plasma

Which of the following can exist in all three states of matter?

a) Water

b) Iron

c) Mercury

d) Gold

Ans:

a) Water

Which law states that at constant temperature, the volume of a gas is inversely proportional to pressure?

a) Charles’ Law

b) Boyle’s Law

c) Avogadro’s Law

d) Dalton’s Law

Ans:

b) Boyle’s Law

Which law states that the volume of a gas is directly proportional to temperature?

a) Charles’ Law

b) Boyle’s Law

c) Avogadro’s Law

d) Dalton’s Law

Ans:

a) Charles’ Law

Which of the following is a homogeneous mixture?

a) Sand and salt

b) Air

c) Oil and water

d) Iron and sulfur

Ans:

b) Air

Which component is called the universal solvent?

a) Alcohol

b) Water

c) Benzene

d) Ether

Ans:

b) Water

Which process is used to separate liquids based on their boiling points?

a) Filtration

b) Distillation

c) Crystallization

d) Sublimation

Ans:

b) Distillation

Which separation technique is used to separate dyes in ink?

a) Filtration

b) Chromatography

c) Sedimentation

d) Distillation

Ans:

b) Chromatography

Which property of a liquid determines its resistance to flow?

a) Surface tension

b) Viscosity

c) Density

d) Pressure

Ans:

b) Viscosity

What is the boiling point of pure water at standard atmospheric pressure?

a) 0°C

b) 50°C

c) 100°C

d) 200°C

Ans:

c) 100°C

Which gas turns limewater milky?

a) Oxygen

b) Carbon dioxide

c) Nitrogen

d) Hydrogen

Ans:

b) Carbon dioxide

Sublimation is a process in which:

a) A solid changes into a gas directly

b) A liquid turns into a gas

c) A gas turns into a solid

d) A liquid turns into a solid

Ans:

a) A solid changes into a gas directly

Which of the following substances undergoes sublimation?

a) Ice

b) Common salt

c) Naphthalene

d) Sand

Ans:

c) Naphthalene

What is the process of a gas turning into a liquid called?

a) Condensation

b) Evaporation

c) Sublimation

d) Melting

Ans:

a) Condensation

What is the density of water at 4°C?

a) 0.5 g/cm³

b) 1 g/cm³

c) 2 g/cm³

d) 10 g/cm³

Ans:

b) 1 g/cm³

Which of the following has the highest density?

a) Oxygen

b) Hydrogen

c) Water

d) Gold

Ans:

d) Gold

Which property of a liquid is responsible for the formation of droplets?

a) Density

b) Viscosity

c) Surface tension

d) Compressibility

Ans:

c) Surface tension

Which element is used in thermometers due to its high expansion rate?

a) Mercury

b) Lead

c) Sodium

d) Iron

Ans:

a) Mercury

Which gas is responsible for the fizz in soft drinks?

a) Oxygen

b) Carbon dioxide

c) Hydrogen

d) Nitrogen

Ans:

b) Carbon dioxide

Which component of air is essential for combustion?

a) Nitrogen

b) Oxygen

c) Carbon dioxide

d) Argon

Ans:

b) Oxygen

What is dry ice?

a) Frozen oxygen

b) Solid carbon dioxide

c) Frozen nitrogen

d) Crushed ice

Ans:

b) Solid carbon dioxide

Which state of matter is lightning composed of?

a) Solid

b) Liquid

c) Gas

d) Plasma

Ans:

d) Plasma

Which of the following is NOT a colloid?

a) Smoke

b) Milk

c) Sugar solution

d) Fog

Ans:

c) Sugar solution

The Tyndall effect is observed in which of the following?

a) True solution

b) Colloidal solution

c) Suspension

d) Both b and c

Ans:

d) Both b and c

4. Chemical Reactions & Metals/Non-Metals (51-75)

Which type of chemical reaction involves the combination of two or more substances to form a new compound?

a) Decomposition reaction

b) Combination reaction

c) Displacement reaction

d) Redox reaction

Ans:

b) Combination reaction

Which type of reaction involves the breakdown of a compound into two or more simpler substances?

a) Combination reaction

b) Decomposition reaction

c) Displacement reaction

d) Redox reaction

Ans:

b) Decomposition reaction

Which metal is the most reactive?

a) Gold

b) Iron

c) Sodium

d) Copper

Ans:

c) Sodium

Which of the following is the least reactive metal?

a) Sodium

b) Potassium

c) Gold

d) Aluminium

Ans:

c) Gold

Which of the following is a noble metal?

a) Copper

b) Zinc

c) Iron

d) Platinum

Ans:

d) Platinum

Which of the following is an alloy?

a) Copper

b) Brass

c) Sodium

d) Mercury

Ans:

b) Brass

Which gas is produced when metals react with acids?

a) Oxygen

b) Hydrogen

c) Carbon dioxide

d) Nitrogen

Ans:

b) Hydrogen

What is the main metal used in electrical wires?

a) Iron

b) Copper

c) Aluminium

d) Lead

Ans:

b) Copper

Which metal is commonly used in making aircraft?

a) Iron

b) Aluminium

c) Copper

d) Zinc

Ans:

b) Aluminium

Which of the following non-metals is a good conductor of electricity?

a) Sulfur

b) Phosphorus

c) Graphite

d) Oxygen

Ans:

c) Graphite

Which process is used to extract metals from their ores?

a) Crystallization

b) Distillation

c) Smelting

d) Evaporation

Ans:

c) Smelting

What is the chemical formula of rust?

a) Fe₂O₃

b) FeO

c) FeSO₄

d) Fe₂O₃·xH₂O

Ans:

d) Fe₂O₃·xH₂O

Which of the following prevents rusting?

a) Galvanization

b) Heating

c) Electrolysis

d) Sublimation

Ans:

a) Galvanization

Which non-metal is essential for breathing?

a) Hydrogen

b) Oxygen

c) Carbon

d) Sulfur

Ans:

b) Oxygen

Which of the following is an amphoteric metal?

a) Aluminium

b) Sodium

c) Potassium

d) Magnesium

Ans:

a) Aluminium

Which metal is liquid at room temperature?

a) Lead

b) Zinc

c) Mercury

d) Aluminium

Ans:

c) Mercury

Which of the following is a metalloid?

a) Sodium

b) Boron

c) Carbon

d) Oxygen

Ans:

b) Boron

Which metal is the best conductor of electricity?

a) Gold

b) Silver

c) Copper

d) Aluminium

Ans:

b) Silver

Which gas is evolved when limestone (CaCO₃) is heated?

a) Oxygen

b) Hydrogen

c) Carbon dioxide

d) Nitrogen

Ans:

c) Carbon dioxide

Which element is the main component of steel?

a) Aluminium

b) Iron

c) Copper

d) Zinc

Ans:

b) Iron

Which metal is used in galvanization?

a) Zinc

b) Copper

c) Silver

d) Aluminium

Ans:

a) Zinc

What is the main component of glass?

a) Silica

b) Limestone

c) Boron

d) Aluminium

Ans:

a) Silica

Which metal is used in thermometers?

a) Iron

b) Mercury

c) Zinc

d) Silver

Ans:

b) Mercury

Which element is used as a semiconductor in electronic devices?

a) Silver

b) Copper

c) Silicon

d) Gold

Ans:

c) Silicon

Which process is used to coat iron with a layer of zinc?

a) Electroplating

b) Galvanization

c) Alloying

d) Tempering

Ans:

b) Galvanization

5. Acids, Bases, Organic Chemistry & Environmental Chemistry (76-100)

Acids, Bases, and Salts

Which acid is commonly found in lemons?

a) Acetic acid

b) Citric acid

c) Sulfuric acid

d) Hydrochloric acid

Ans:

b) Citric acid

Which of the following is a strong acid?

a) Acetic acid

b) Hydrochloric acid

c) Carbonic acid

d) Boric acid

Ans:

b) Hydrochloric acid

What is the pH value of pure water?

a) 5

b) 6

c) 7

d) 8

Ans:

c) 7

Which base is commonly used in soap making?

a) Sodium hydroxide

b) Calcium hydroxide

c) Ammonium hydroxide

d) Potassium chloride

Ans:

a) Sodium hydroxide

Which indicator turns red in acidic solutions and blue in basic solutions?

a) Methyl orange

b) Phenolphthalein

c) Litmus

d) Bromothymol blue

Ans:

c) Litmus

Which salt is commonly known as baking soda?

a) Sodium chloride

b) Sodium bicarbonate

c) Sodium carbonate

d) Calcium carbonate

Ans:

b) Sodium bicarbonate

What is the chemical name of table salt?

a) Sodium bicarbonate

b) Sodium chloride

c) Sodium sulfate

d) Potassium chloride

Ans:

b) Sodium chloride

Which acid is used in car batteries?

a) Nitric acid

b) Hydrochloric acid

c) Sulfuric acid

d) Acetic acid

Ans:

c) Sulfuric acid

Which base is commonly known as slaked lime?

a) Sodium hydroxide

b) Calcium hydroxide

c) Ammonium hydroxide

d) Magnesium hydroxide

Ans:

b) Calcium hydroxide

Which gas is released when acids react with metals?

a) Oxygen

b) Nitrogen

c) Hydrogen

d) Carbon dioxide

Ans:

c) Hydrogen

Organic Chemistry

Which element is the basis of organic chemistry?

a) Hydrogen

b) Oxygen

c) Carbon

d) Nitrogen

Ans:

c) Carbon

Which hydrocarbon is used as cooking gas?

a) Methane

b) Propane

c) Butane

d) Both b and c

Ans:

d) Both b and c

Which of the following is an unsaturated hydrocarbon?

a) Methane

b) Ethane

c) Ethene

d) Propane

Ans:

c) Ethene

Which compound is commonly known as wood alcohol?

a) Ethanol

b) Methanol

c) Propanol

d) Butanol

Ans:

b) Methanol

Which compound is used as an antiseptic in hospitals?

a) Chloroform

b) Ethanol

c) Acetone

d) Phenol

Ans:

d) Phenol

Which polymer is used in making plastic bags?

a) Polystyrene

b) Polyethylene

c) Polyvinyl chloride

d) Nylon

Ans:

b) Polyethylene

Which type of alcohol is present in alcoholic beverages?

a) Methanol

b) Ethanol

c) Propanol

d) Butanol

Ans:

b) Ethanol

What is the functional group of alcohols?

a) -CHO

b) -OH

c) -COOH

d) -NH₂

Ans:

b) -OH

Which hydrocarbon is used in welding?

a) Methane

b) Ethylene

c) Acetylene

d) Propane

Ans:

c) Acetylene

What is the main component of natural gas?

a) Ethane

b) Propane

c) Methane

d) Butane

Ans:

c) Methane

Environmental Chemistry

Which gas is mainly responsible for acid rain?

a) Oxygen

b) Sulfur dioxide

c) Methane

d) Nitrogen

Ans:

b) Sulfur dioxide

Which pollutant is responsible for ozone layer depletion?

a) Carbon dioxide

b) CFCs (Chlorofluorocarbons)

c) Methane

d) Nitrogen oxides

Ans:

b) CFCs (Chlorofluorocarbons)

Which greenhouse gas has the highest global warming potential?

a) Carbon dioxide

b) Methane

c) Water vapor

d) Nitrous oxide

Ans:

b) Methane

Which gas is released in large amounts by burning fossil fuels?

a) Oxygen

b) Carbon dioxide

c) Ozone

d) Nitrogen

Ans:

b) Carbon dioxide

Which element is essential for the process of photosynthesis?

a) Nitrogen

b) Phosphorus

c) Carbon

d) Magnesium

Ans:

d) Magnesium