chemistry MCQs

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chemistry MCQs

Practice complete Chemistry MCQs covering Matter, States of Matter, Physical and Chemical Changes, Atomic Structure, Chemical Bonding, Periodic Table, Acids, Bases and Salts, Metals and Non-Metals, Chemical Reactions, Electrochemistry, Organic Chemistry, Hydrocarbons, Environmental Chemistry, Polymers, Biomolecules, Nuclear Chemistry, and all other important topics. Includes chapter-wise and exam-oriented multiple-choice questions with detailed answers and explanations for JKSSB, SSC, Banking, Railway, UPSC, CUET, NEET, State PSCs, and other competitive exams.

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Question #581
Which of the following is a characteristic of covalent compounds?
A. Low melting and boiling points
B. Good conductors of electricity
C. High melting and boiling points
D. Soluble in water
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Correct Answer: Option A

Explanation:
Covalent compounds generally have low melting and boiling points because the intermolecular forces (van der Waals forces) holding the molecules together are relatively weak compared to the strong ionic bonds in ionic compounds. They are also generally poor conductors of electricity as they lack free ions.
This question belongs to: Science chemistry
Question #582
Assertion (A): Micelle formation occurs when soap is dissolved in water. Reason (R): The hydrophobic tails of soap molecules cluster together to avoid water, while the hydrophilic heads face outward.
A. A is false but R is true.
B. Both A and R are true and R is the correct explanation of A.
C. Both A and R are true but R is NOT the correct explanation of A.
D. A is true but R is false.
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Correct Answer: Option B

Explanation:
In water, soap molecules arrange themselves into spherical aggregates called micelles. The hydrophobic hydrocarbon tails point inward, away from water, while the hydrophilic ionic heads point outward, interacting with water. This structure traps oily dirt in the center, allowing it to be washed away.
This question belongs to: Science chemistry
Question #583
The main component of LPG is:
A. Methane
B. Ethane
C. Propane
D. Butane
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Correct Answer: Option D

Explanation:
Liquefied Petroleum Gas (LPG) primarily consists of butane (C₄H₁₀) and isobutane, with some propane. For domestic use, it is often a mix of butane and propane. Methane is the main component of CNG and natural gas, which require different storage pressures and infrastructure.
This question belongs to: Science chemistry
Question #584
The calorific value of a fuel is defined as:
A. The amount of oxygen required for combustion.
B. The total amount of fuel available.
C. The temperature at which the fuel catches fire.
D. The amount of heat produced by complete combustion of 1 kg of fuel.
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Correct Answer: Option D

Explanation:
Calorific value is the amount of heat energy produced on the complete combustion of 1 kg (or 1 m³ for gases) of a fuel. It is expressed in kJ/kg or kJ/m³. Hydrogen has the highest calorific value among common fuels, making it a highly efficient energy source.
This question belongs to: Science chemistry
Question #585
CNG stands for:
A. Carbon Natural Gas
B. Compressed Natural Gas
C. Condensed Natural Gas
D. Clean Natural Gas
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Correct Answer: Option B

Explanation:
CNG stands for Compressed Natural Gas. It is primarily methane stored at high pressure. It is considered a cleaner fuel than petrol or diesel because it produces fewer pollutants like carbon monoxide and unburnt hydrocarbons, and it leaves no residue upon combustion.
This question belongs to: Science chemistry
Question #586
Which of the following is considered the cleanest fuel?
A. Wood
B. Hydrogen
C. Coal
D. Diesel
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Correct Answer: Option B

Explanation:
Hydrogen is considered the cleanest fuel because its combustion produces only water (2H₂ + O₂ → 2H₂O) and no greenhouse gases or toxic pollutants. Coal, wood, and diesel produce CO₂, CO, SO₂, and particulate matter, contributing significantly to air pollution and global warming.
This question belongs to: Science chemistry
Question #587
The process of heating coal in the absence of air to produce coal gas, coal tar, and coke is called:
A. Fractional distillation
B. Carbonization
C. Cracking
D. Destructive distillation
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Correct Answer: Option D

Explanation:
Destructive distillation is the process of heating a carbon-containing substance (like coal or wood) in the absence of air to break it down into various products. For coal, it yields coke, coal tar, coal gas, and coal dust. Fractional distillation is used for separating liquid mixtures like petroleum.
This question belongs to: Science chemistry
Question #588
Which gas is primarily responsible for the greenhouse effect from burning fossil fuels?
A. Oxygen
B. Carbon dioxide
C. Hydrogen
D. Nitrogen
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Correct Answer: Option B

Explanation:
Carbon dioxide (CO₂) is the primary greenhouse gas emitted from the burning of fossil fuels (coal, oil, natural gas). It traps heat in the Earth's atmosphere, leading to global warming. Oxygen, nitrogen, and hydrogen do not absorb infrared radiation and thus do not contribute to the greenhouse effect.
This question belongs to: Science chemistry
Question #589
Assertion (A): Hydrogen is a better fuel than CNG. Reason (R): Hydrogen is highly explosive and difficult to store safely.
A. A is true but R is false.
B. A is false but R is true.
C. Both A and R are true but R is NOT the correct explanation of A.
D. Both A and R are true and R is the correct explanation of A.
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Correct Answer: Option C

Explanation:
Hydrogen has a higher calorific value than CNG, making it a better fuel in terms of energy output per unit mass. However, R states it is explosive and hard to store, which is a disadvantage, not the reason it is a better fuel. Thus, both are true, but R does not explain A.
This question belongs to: Science chemistry
Question #590
The ignition temperature of a fuel is:
A. The temperature at which it melts.
B. The lowest temperature at which it catches fire.
C. The highest temperature it can reach.
D. The temperature at which it boils.
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Correct Answer: Option B

Explanation:
The ignition temperature (or kindling temperature) is the minimum temperature to which a fuel must be heated so that it catches fire and starts burning spontaneously. A lower ignition temperature means the fuel is more highly flammable and can ignite more easily at ambient conditions.
This question belongs to: Science chemistry
Question #591
The process of depositing a thin layer of a metal on an object using electricity is called:
A. Electrolysis
B. Electroplating
C. Electrorefining
D. Electrometallurgy
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Correct Answer: Option B

Explanation:
Electroplating is the application of electrolytic cells to deposit a thin, protective, or decorative layer of a metal (like gold, silver, or chromium) onto a conductive object. Electrolysis is the general process of using electricity to drive a non-spontaneous chemical reaction.
This question belongs to: Science chemistry
Question #592
In the electrolysis of acidified water, the gas collected at the cathode is:
A. Chlorine
B. Oxygen
C. Nitrogen
D. Hydrogen
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Correct Answer: Option D

Explanation:
During the electrolysis of water, reduction occurs at the cathode (negative electrode), where H⁺ ions gain electrons to form hydrogen gas (2H⁺ + 2e⁻ → H₂). Oxidation occurs at the anode, producing oxygen gas. The volume of H₂ collected is exactly twice that of O₂.
This question belongs to: Science chemistry
Question #593
Which of Faraday's laws of electrolysis states that the mass of substance deposited is directly proportional to the quantity of electricity passed?
A. Third Law
B. Law of Conservation of Mass
C. First Law
D. Second Law
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Correct Answer: Option C

Explanation:
Faraday's First Law of Electrolysis states that the mass of a substance deposited or liberated at an electrode is directly proportional to the total charge (Q) passed through the electrolyte (m = ZQ, where Z is the electrochemical equivalent). The Second Law relates mass to equivalent weight.
This question belongs to: Science chemistry
Question #594
An electrochemical cell that converts chemical energy into electrical energy is called:
A. Galvanic cell
B. Daniel cell
C. Electrolytic cell
D. Both B and C
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Correct Answer: Option D

Explanation:
A galvanic (or voltaic) cell generates electrical energy from a spontaneous chemical reaction. The Daniel cell is a specific, classic type of galvanic cell using zinc and copper electrodes. An electrolytic cell does the reverse, using electrical energy to drive a non-spontaneous chemical reaction.
This question belongs to: Science chemistry
Question #595
In a Daniel cell, the anode is made of:
A. Copper
B. Graphite
C. Zinc
D. Platinum
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Correct Answer: Option C

Explanation:
In a Daniel cell, the anode (where oxidation occurs) is a zinc rod immersed in ZnSO₄ solution. The cathode is a copper rod in CuSO₄ solution. Zinc is more reactive, so it loses electrons (Zn → Zn²⁺ + 2e⁻) and acts as the negative terminal of the cell.
This question belongs to: Science chemistry
Question #596
Which of the following is an electrolyte?
A. Distilled water
B. Sugar solution
C. Ethanol
D. Aqueous solution of NaCl
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Correct Answer: Option D

Explanation:
An electrolyte is a substance that produces ions when dissolved in water or melted, allowing the solution to conduct electricity. Aqueous NaCl dissociates into Na⁺ and Cl⁻ ions. Distilled water, sugar, and ethanol do not form ions in solution and are therefore non-electrolytes.
This question belongs to: Science chemistry
Question #597
Assertion (A): Pure water is a bad conductor of electricity. Reason (R): Pure water does not contain any dissolved ions.
A. Both A and R are true but R is NOT the correct explanation of A.
B. A is false but R is true.
C. Both A and R are true and R is the correct explanation of A.
D. A is true but R is false.
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Correct Answer: Option C

Explanation:
Pure water consists only of H₂O molecules, which barely dissociate into H⁺ and OH⁻ ions (10⁻⁷ M). Due to the extreme lack of free ions, it is a very poor conductor. Adding acids, bases, or salts provides ions, making it a good conductor. Both statements are correct and R explains A.
This question belongs to: Science chemistry
Question #598
During electroplating of silver on a copper spoon, the electrolyte used is:
A. Sodium chloride solution
B. Silver nitrate solution
C. Copper nitrate solution
D. Copper sulfate solution
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Correct Answer: Option B

Explanation:
In electroplating, the electrolyte must contain the ions of the metal to be deposited. To plate silver, a solution of a silver salt, such as silver nitrate (AgNO₃) or silver cyanide, is used. The anode is pure silver, and the cathode is the copper spoon to be plated.
This question belongs to: Science chemistry
Question #599
Which of the following is used as an inert electrode in electrolysis?
A. Copper
B. Zinc
C. Silver
D. Platinum
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Correct Answer: Option D

Explanation:
Inert electrodes do not participate in the chemical reaction; they merely provide a surface for electron transfer. Platinum and graphite are common inert electrodes. Copper, zinc, and silver are active electrodes and can dissolve or deposit during electrolysis, thereby participating in the chemical change.
This question belongs to: Science chemistry
Question #600
Boyle's law states that at constant temperature, the pressure of a fixed mass of gas is:
A. Directly proportional to its volume.
B. Inversely proportional to its mass.
C. Inversely proportional to its volume.
D. Directly proportional to its mass.
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Correct Answer: Option C

Explanation:
Boyle's Law states that for a fixed mass of gas at constant temperature, pressure is inversely proportional to volume (P ∝ 1/V, or PV = constant). As volume decreases, gas molecules hit the container walls more frequently, increasing the pressure exerted by the gas.
This question belongs to: Science chemistry

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