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 #1041
Assertion (A): At absolute zero, the volume of an ideal gas becomes zero. Reason (R): At absolute zero, the kinetic energy of the gas molecules is zero.
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
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Correct Answer: Option A

Explanation:
According to Charles's Law (V ∝ T), extrapolating the volume-temperature graph of an ideal gas to absolute zero (0 K) yields a volume of zero. At 0 K, the theoretical kinetic energy of molecules is zero, meaning they stop moving. Both are true, but the zero volume is a mathematical extrapolation of the gas law, not a direct physical consequence of zero kinetic energy alone, as real gases liquefy first.
This question belongs to: Science chemistry
Question #1042
The critical temperature of a gas is the temperature:
A. At which its volume becomes zero.
B. Below which it cannot be liquefied by pressure alone.
C. At which it solidifies.
D. Above which it cannot be liquefied by pressure alone.
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Correct Answer: Option D

Explanation:
The critical temperature (Tc) is the temperature above which a gas cannot be liquefied, regardless of how much pressure is applied. Above Tc, the kinetic energy of the molecules is too high for intermolecular forces to hold them together in a liquid state, even under extreme pressure.
This question belongs to: Science chemistry
Question #1043
Which of the following is an example of a homogeneous catalyst?
A. Platinum in Ostwald's process
B. Iron in Haber's process
C. Sulphuric acid in esterification
D. Nickel in hydrogenation of oils
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Correct Answer: Option C

Explanation:
A homogeneous catalyst is in the same phase as the reactants. In the esterification of carboxylic acids with alcohols, liquid sulfuric acid (H2SO4) catalyzes the reaction between liquid reactants. Iron, platinum, and nickel are solid catalysts used for gaseous or liquid reactants, making them heterogeneous catalysts.
This question belongs to: Science chemistry
Question #1044
The phenomenon where a product of a reaction acts as a catalyst for the same reaction is called:
A. Negative catalysis
B. Autocatalysis
C. Heterogeneous catalysis
D. Enzyme catalysis
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Correct Answer: Option B

Explanation:
Autocatalysis occurs when one of the products of a chemical reaction acts as a catalyst for that same reaction. As the reaction proceeds and the product accumulates, the rate of the reaction increases. A classic example is the oxidation of oxalic acid by potassium permanganate, where the Mn2+ ions produced catalyze the reaction.
This question belongs to: Science chemistry
Question #1045
Which of the following is an example of catalytic poisoning?
A. Addition of phosphoric acid to slow down H2O2 decomposition.
B. Addition of molybdenum to iron in Haber's process.
C. Platinum increasing the rate of combustion of hydrogen.
D. Arsenic ruining the activity of finely divided iron in Haber's process.
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Correct Answer: Option D

Explanation:
Catalytic poisoning occurs when a substance (a catalytic poison) binds strongly to the active sites of a catalyst, blocking reactants from adsorbing and thereby destroying or reducing its catalytic activity. Arsenic acts as a poison for the iron catalyst used in the Haber process for ammonia synthesis.
This question belongs to: Science chemistry
Question #1046
In the Contact process, the catalyst used is:
A. Nitric oxide
B. Vanadium pentoxide
C. Finely divided Iron
D. Platinum
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Correct Answer: Option B

Explanation:
The Contact process is used for the industrial manufacture of sulfuric acid. The key step is the oxidation of sulfur dioxide (SO2) to sulfur trioxide (SO3). This reaction is catalyzed by Vanadium pentoxide (V2O5). Platinum was historically used but was replaced by V2O5 because it is cheaper and less susceptible to poisoning.
This question belongs to: Science chemistry
Question #1047
The process of concentrating an ore by taking advantage of the difference in density between the ore and the gangue is:
A. Magnetic separation
B. Froth flotation
C. Leaching
D. Hydraulic washing
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Correct Answer: Option D

Explanation:
Hydraulic washing, also known as gravity separation, is based on the difference in specific gravities (densities) of the metallic ore and the associated impurities (gangue). The powdered ore is washed with a running stream of water; the lighter impurities are carried away, leaving the heavier ore particles behind.
This question belongs to: Science chemistry
Question #1048
Which of the following metals is extracted by the thermite process?
A. Chromium
B. Aluminum
C. Iron
D. All of the above
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Correct Answer: Option D

Explanation:
The thermite process involves the reduction of a metal oxide by aluminum powder, which is highly exothermic. It is used to extract metals like chromium, manganese, and iron from their oxides (e.g., Cr2O3 + 2Al -> 2Cr + Al2O3). It is also practically used for welding iron railway tracks.
This question belongs to: Science chemistry
Question #1049
In the froth flotation process, the depressant is used to:
A. Enhance the froth formation of all minerals.
B. Dissolve the ore.
C. Increase the density of the gangue.
D. Prevent one specific mineral from coming to the froth.
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Correct Answer: Option D

Explanation:
Froth flotation separates sulfide ores from gangue based on their wetting properties. Sometimes, an ore contains multiple sulfides. A depressant (like NaCN) is added to selectively prevent one mineral (e.g., FeS2) from attaching to the froth, allowing only the desired mineral (e.g., PbS) to be separated.
This question belongs to: Science chemistry
Question #1050
The reduction of a metal oxide by carbon at high temperature is known as:
A. Roasting
B. Calcination
C. Leaching
D. Smelting
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Correct Answer: Option D

Explanation:
Smelting is the pyrometallurgical process of extracting a metal from its ore by heating it beyond its melting point and reducing the metal oxide with a carbonaceous reducing agent (like coke or coal). Flux is often added to remove impurities as slag. Calcination and roasting are oxidation processes.
This question belongs to: Science chemistry
Question #1051
Which of the following is a method of refining (purification) of metals?
A. Liquation
B. All of the above
C. Poling
D. Zone refining
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Correct Answer: Option B

Explanation:
Refining is the final step in metallurgy to obtain pure metal. Poling is used for copper to remove oxide impurities. Liquation separates low-melting metals (like tin) from high-melting impurities. Zone refining is used for producing ultra-pure semiconductors (like Si, Ge) based on the principle that impurities are more soluble in the molten state.
This question belongs to: Science chemistry
Question #1052
Assertion (A): Zinc can displace copper from copper sulfate solution. Reason (R): Zinc is more reactive than copper.
A. A is false but R is true.
B. A is true but R is false.
C. Both A and R are true and R is the correct explanation of A.
D. Both A and R are true but R is NOT the correct explanation of A.
Discuss
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Correct Answer: Option C

Explanation:
In the electrochemical series, zinc is placed above copper, meaning it has a higher oxidation potential (is more reactive). A more reactive metal can displace a less reactive metal from its aqueous salt solution. Therefore, zinc displaces copper from CuSO4, forming ZnSO4 and depositing Cu metal. R correctly explains A.
This question belongs to: Science chemistry
Question #1053
Which of the following fertilizers provides both nitrogen and phosphorus?
A. Ammonium sulfate
B. Urea
C. Diammonium phosphate (DAP)
D. Muriate of potash
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Correct Answer: Option C

Explanation:
Diammonium phosphate (DAP), with the formula (NH4)2HPO4, is a widely used complex fertilizer. It provides two essential macronutrients: nitrogen (from the ammonium ion) and phosphorus (from the phosphate ion). Urea and ammonium sulfate provide only nitrogen, while muriate of potash provides potassium.
This question belongs to: Science chemistry
Question #1054
Which bacterium is responsible for converting ammonia into nitrites in the nitrogen cycle?
A. Nitrosomonas
B. Rhizobium
C. Nitrobacter
D. Azotobacter
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Correct Answer: Option A

Explanation:
Nitrification is a two-step aerobic process in the nitrogen cycle. First, ammonia (NH3) is oxidized to nitrites (NO2-) by bacteria like Nitrosomonas and Nitrosococcus. In the second step, nitrites are oxidized to nitrates (NO3-) by Nitrobacter. Rhizobium fixes nitrogen, and Azotobacter is a free-living nitrogen fixer.
This question belongs to: Science chemistry
Question #1055
Consider the following statements: 1. NPK fertilizers contain only macronutrients. 2. Zinc and Boron are micronutrients for plants. Which is/are correct?
A. Both 1 and 2
B. Neither 1 nor 2
C. 2 only
D. 1 only
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Correct Answer: Option A

Explanation:
NPK fertilizers supply the three primary macronutrients: Nitrogen (N), Phosphorus (P), and Potassium (K). Plants also require trace elements (micronutrients) in very small amounts for proper growth, such as Iron, Manganese, Zinc, Copper, Boron, and Molybdenum. Both statements are factually correct.
This question belongs to: Science chemistry
Question #1056
Green manure is obtained from:
A. Chemical synthesis
B. Animal waste
C. Decomposed plant material
D. Fungal cultures
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Correct Answer: Option C

Explanation:
Green manure refers to crops (like sunn hemp or dhaincha) that are grown specifically to be plowed back into the soil while they are still green. This decomposing plant material enriches the soil with organic matter, nitrogen, and other nutrients, improving soil structure and fertility.
This question belongs to: Science chemistry
Question #1057
The main component of single superphosphate is:
A. Ca3(PO4)2
B. Both A and C
C. CaSO4
D. Ca(H2PO4)2
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Correct Answer: Option B

Explanation:
Single superphosphate (SSP) is manufactured by treating rock phosphate with sulfuric acid. The resulting product is a mixture of calcium dihydrogen phosphate (Ca(H2PO4)2), which is the actual fertilizer providing soluble phosphorus, and calcium sulfate (CaSO4, gypsum), which is an inactive filler.
This question belongs to: Science chemistry
Question #1058
The chemical formula of oleum is:
A. H2SO3
B. H2S2O8
C. H2S2O7
D. H2SO4
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Correct Answer: Option C

Explanation:
Oleum, also known as fuming sulfuric acid, is a solution of sulfur trioxide (SO3) in concentrated sulfuric acid (H2SO4). Its chemical formula is often represented as H2S2O7 (disulfuric acid or pyrosulfuric acid), which is essentially H2SO4 + SO3. It is an intermediate in the Contact process.
This question belongs to: Science chemistry
Question #1059
In the Ostwald process, the catalyst used for the oxidation of ammonia is:
A. Iron
B. Vanadium pentoxide
C. Platinum
D. Nickel
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Correct Answer: Option C

Explanation:
The Ostwald process is used to manufacture nitric acid. The first step involves the catalytic oxidation of ammonia (NH3) to nitric oxide (NO). This reaction is carried out at about 800°C using a platinum-rhodium gauge catalyst. Iron is used in the Haber process, and V2O5 in the Contact process.
This question belongs to: Science chemistry
Question #1060
Which acid is known as 'Aqua Fortis'?
A. Sulfuric acid
B. Hydrochloric acid
C. Acetic acid
D. Nitric acid
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Correct Answer: Option D

Explanation:
Nitric acid (HNO3) is historically known as Aqua Fortis, which translates to 'strong water' in Latin. This name was given by early alchemists due to its ability to dissolve almost all metals, including silver, which was not dissolved by other known acids at the time.
This question belongs to: Science chemistry

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