chemistry MCQs

Science

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.

1089
Total Questions

Practice Questions

Page 6 of 55
Question #101
Which of the following allotropes of carbon is used as a lubricant?
A. Coal
B. Diamond
C. Graphite
D. Fullerene
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Graphite's layered structure with weak van der Waals forces between layers allows them to slide over each other, making it a good dry lubricant. It is used in machines where oil cannot be used (high temperature) or in pencil lead mixed with clay. Diamond is hard, used as abrasive. Fullerenes are nanomaterials, not lubricants. Coal is fuel.
This question belongs to: Science chemistry
Question #102
Methane on complete combustion with excess oxygen yields:
A. CO and H₂O
B. CO₂ and H₂O
C. CO₂ and H₂
D. C and H₂O
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
CH₄ + 2O₂ → CO₂ + 2H₂O + heat. Complete combustion of any hydrocarbon with sufficient oxygen always produces carbon dioxide and water. Incomplete combustion due to limited oxygen produces carbon monoxide (CO) and/or soot (carbon particles). Methane is the main component of natural gas and biogas. CO is a poisonous gas. The combustion of alkanes is highly exothermic.
This question belongs to: Science chemistry
Question #103
Which fuel has the highest calorific value per gram?
A. Hydrogen
B. Methane
C. Coal
D. Wood
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Hydrogen has the highest calorific value (~150 kJ/g or 141.9 MJ/kg) because it has no heavier atoms like carbon and its combustion produces water, a very stable product. Methane ~55.5 kJ/g, coal ~25-35 kJ/g, wood ~17 kJ/g. Hydrogen is a clean fuel, but storage and production challenges remain. It can be used in fuel cells or internal combustion engines.
This question belongs to: Science chemistry
Question #104
In an electrochemical cell, the salt bridge is used to:
A. Increase electrode potential
B. Prevent corrosion
C. Complete the circuit and maintain electrical neutrality
D. Increase current
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
The salt bridge (e.g., KCl-agar) allows migration of ions between half-cells, completing the circuit and maintaining charge neutrality. Without it, charge buildup would stop the reaction. It does not increase current or electrode potential. It prevents mixing of solutions. A porous membrane can also serve. Ions in the bridge must have similar mobility and not interfere with cell reactions.
This question belongs to: Science chemistry
Question #105
Faraday's second law of electrolysis relates the masses of different substances deposited to their:
A. Molecular masses
B. Atomic masses
C. Equivalent weights
D. Densities
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Faraday's second law: When the same quantity of electricity is passed through different electrolytes, the masses of substances deposited are proportional to their equivalent weights (E). m₁/m₂ = E₁/E₂. Equivalent weight = atomic mass / valency (or change in oxidation number). This law is used to calculate the amount of metal deposited or gas liberated. Electrolysis is quantitative.
This question belongs to: Science chemistry
Question #106
A gas occupies 2.0 L at 1.0 atm. If pressure is increased to 4.0 atm at constant temperature, the volume will be:
A. 1.0 L
B. 8.0 L
C. 0.5 L
D. 2.0 L
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option C

Explanation:
Boyle's law: P₁V₁ = P₂V₂. Given P₁=1.0 atm, V₁=2.0 L, P₂=4.0 atm. V₂ = (1.0 × 2.0) / 4.0 = 0.5 L. Volume decreases as pressure increases, because gas is compressible. The product PV is constant for a fixed mass of gas at constant T. Scuba divers experience this; as they dive deeper, pressure increases, reducing air volume in lungs.
This question belongs to: Science chemistry
Question #107
The ideal gas equation PV = nRT can be derived by combining which three laws?
A. Avogadro's, Dalton's, and Boyle's law
B. Boyle's, Graham's, and Dalton's law
C. Charles', Graham's, and Gay-Lussac's law
D. Boyle's, Charles', and Avogadro's law
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Ideal gas equation: PV = nRT is obtained by combining Boyle's law (PV = constant at T,n), Charles' law (V ∝ T at P,n), and Avogadro's law (V ∝ n at P,T). Graham's law deals with diffusion, Dalton's with partial pressures. The constant R is the universal gas constant. For 1 mole, PV = RT. Real gases deviate at high pressure and low temperature.
This question belongs to: Science chemistry
Question #108
Which catalyst is used in the decomposition of KClO₃ to prepare oxygen in the laboratory?
A. Pt
B. Fe₂O₃
C. V₂O₅
D. MnO₂
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Manganese dioxide (MnO₂) catalyzes the thermal decomposition of potassium chlorate: 2KClO₃ (heat, MnO₂) → 2KCl + 3O₂. Without MnO₂, decomposition requires higher temperature. MnO₂ is not consumed. Other catalysts can be used, but MnO₂ is standard in school labs. V₂O₅ is for SO₂ oxidation, Pt for various, Fe₂O₃ not typical. This is a simple preparation of oxygen.
This question belongs to: Science chemistry
Question #109
Enzymes in yeast catalyze the conversion of glucose to ethanol. This is an example of:
A. Fermentation
B. Oxidation
C. Saponification
D. Esterification
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Fermentation is an anaerobic biological process in which enzymes (zymase) convert glucose to ethanol and CO₂: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. Oxidation would require oxygen. Esterification forms esters, saponification makes soap. Fermentation is used in brewing, winemaking, and baking (where CO₂ makes bread rise). The temperature is kept around 30-35°C.
This question belongs to: Science chemistry
Question #110
Which of the following is a biofertilizer?
A. Rhizobium
B. Urea
C. Ammonium sulfate
D. Superphosphate
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Rhizobium is a nitrogen-fixing bacterium that lives in root nodules of legumes and converts atmospheric N₂ to ammonia, enriching soil fertility naturally. It is a biofertilizer. Urea and ammonium sulfate are synthetic nitrogenous fertilizers. Superphosphate is a synthetic phosphorus fertilizer. Biofertilizers like Azotobacter, Blue-green algae, and mycorrhizae are eco-friendly and sustainable.
This question belongs to: Science chemistry
Question #111
The chemical name of baking soda is:
A. Potassium carbonate
B. Sodium carbonate
C. Calcium carbonate
D. Sodium hydrogen carbonate
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Baking soda is sodium hydrogen carbonate (NaHCO₃). It is used as a leavening agent in baking (produces CO₂ upon heating or with acid), as an antacid, and in fire extinguishers. Sodium carbonate (Na₂CO₃) is washing soda. Calcium carbonate is limestone/marble. Potassium carbonate is potash. Baking powder is a mixture of NaHCO₃ and a weak acid like tartaric acid.
This question belongs to: Science chemistry
Question #112
Assertion (A): A reaction between an acid and a base is called a neutralization reaction. Reason (R): Neutralization always produces a neutral solution with pH exactly 7.
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
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Neutralization is the reaction of an acid with a base to produce salt and water. However, the resulting solution is not always neutral (pH 7) because the salt may undergo hydrolysis. If the acid is strong and base weak (e.g., HCl + NH₄OH), the salt (NH₄Cl) is acidic, pH < 7. If acid is weak and base strong (CH₃COOH + NaOH), salt is basic, pH > 7. Only strong acid-strong base gives pH 7.
This question belongs to: Science chemistry
Question #113
The indicator phenolphthalein turns pink in:
A. All media
B. Basic medium
C. Acidic medium
D. Neutral medium
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Phenolphthalein is colorless in acidic and neutral solutions, turning pink/magenta in basic solutions with pH > about 8.2-10. It is commonly used in acid-base titrations. Methyl orange is red in acidic and yellow in basic. Litmus is purple in neutral, red in acid, blue in base. Natural indicators like turmeric, beetroot also show color changes.
This question belongs to: Science chemistry
Question #114
Which gas is produced when zinc reacts with dilute hydrochloric acid?
A. Hydrogen
B. Oxygen
C. Chlorine
D. Carbon dioxide
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Zn + 2HCl → ZnCl₂ + H₂↑. Zinc displaces hydrogen from acid because it is more reactive than hydrogen in the reactivity series. Hydrogen gas burns with a pop sound when a burning splint is brought near the mouth of the test tube. Metals above hydrogen in the series react with acids to evolve H₂; metals below (Cu, Ag) do not. Nitric acid is an oxidizer, so may not yield H₂.
This question belongs to: Science chemistry
Question #115
Which of the following alloys contains copper and zinc?
A. Brass
B. Solder
C. Steel
D. Bronze
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Brass is an alloy of copper (Cu) and zinc (Zn). Proportions vary to give different properties; common brass is 70% Cu, 30% Zn. Bronze is primarily Cu and Sn (tin). Solder is Pb and Sn. Steel is Fe with C and other elements. Brass is used for musical instruments, plumbing, and decorative hardware due to its gold-like appearance and corrosion resistance.
This question belongs to: Science chemistry
Question #116
Which of the following is a polymer of vinyl chloride?
A. Nylon
B. PVC
C. Polythene
D. Teflon
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
PVC (polyvinyl chloride) is an addition polymer of vinyl chloride monomer (CH₂=CHCl). It is used for pipes, cables, flooring, and medical equipment. Teflon from tetrafluoroethene, polythene from ethylene, nylon is a polyamide (condensation polymer). PVC can be rigid or flexible depending on plasticizers added. It is a thermoplastic. Disposal of PVC by burning produces toxic HCl gas.
This question belongs to: Science chemistry
Question #117
Which of the following is an example of a condensation polymer?
A. PVC
B. Teflon
C. Polythene
D. Nylon-6,6
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Nylon-6,6 is a condensation polymer formed by reaction between hexamethylenediamine and adipic acid, with elimination of water molecules. Polythene, Teflon, and PVC are addition polymers where monomers add without loss of small molecules. Condensation polymers often have amide or ester linkages. Another example is polyester (terylene). Nylon is a polyamide, known for strength and elasticity.
This question belongs to: Science chemistry
Question #118
The process of converting vegetable oils to solid fats (vanaspati) involves:
A. Saponification
B. Hydrogenation
C. Esterification
D. Fermentation
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option B

Explanation:
Hydrogenation adds hydrogen to unsaturated vegetable oils in the presence of nickel catalyst at about 150°C, converting liquid oils (C=C bonds) to solid fats (vanaspati ghee) with higher melting points. Saponification makes soap. Esterification forms esters. Fermentation produces alcohol. Partial hydrogenation can produce trans fats, which are harmful. Complete hydrogenation yields saturated fats.
This question belongs to: Science chemistry
Question #119
The main component of cement that is responsible for the initial setting is:
A. Tricalcium aluminate
B. Dicalcium silicate
C. Tricalcium silicate
D. Tetracalcium aluminoferrite
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option A

Explanation:
Tricalcium aluminate (C₃A) reacts quickly with water and is responsible for the flash setting of cement. Gypsum is added to control the rate of this initial set. Tricalcium silicate (C₃S) provides early strength. Dicalcium silicate (C₂S) gives later strength. Tetracalcium aluminoferrite (C₄AF) contributes to color and hardness. Cement composition is abbreviated in cement chemistry notation.
This question belongs to: Science chemistry
Question #120
The addition of gypsum to cement clinker during grinding:
A. Decreases strength
B. Decreases setting time
C. Increases color
D. Increases setting time
Discuss
Get Complete Subject PDF for Science

Correct Answer: Option D

Explanation:
Gypsum (CaSO₄·2H₂O) is added to clinker to control the rapid reaction of tricalcium aluminate with water, which would otherwise cause flash (quick) setting. Gypsum slows down the hydration of C₃A, thus increasing the setting time and allowing workability. Without gypsum, cement would set almost immediately upon mixing with water, making placement impossible.
This question belongs to: Science chemistry

More Science Topics

Biology MCQs
Physics MCQs
Today's Top Topics
Biology 2054 Physics 1287 chemistry 1089
Explore Subjects
Computer 5279 Maths 5575 Accountancy and Statistics 3179 Science 4430 Static General Knowledge 6362
Practice Mix
Which of the following describes a precompiled collection of SQL statements stored on the database server that can be executed repeatedly by name?
Which major corporate computing entity was founded directly from the evolution of Herman Hollerith’s Tabulating Machine Company?
Total Fertility Rate (TFR) of 2.5 indicates that, on average, women are having:
Choose the antonym of 'YEARNING'.
The median of the dataset: 10, 15, 20, 25, 30, 35 is: