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 #621
Which of the following metals is extracted by electrolytic reduction?
A. Sodium
B. Copper
C. Iron
D. Zinc
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Correct Answer: Option A

Explanation:
Highly reactive metals like sodium, potassium, calcium, and aluminum cannot be reduced by chemical reducing agents like carbon. They are extracted by the electrolysis of their molten chlorides or oxides. For example, sodium is extracted by the electrolysis of molten NaCl in the Down's cell.
This question belongs to: Science chemistry
Question #622
The impurities present in an ore are known as:
A. Gangue
B. Flux
C. Matrix
D. Slag
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Correct Answer: Option A

Explanation:
The unwanted earthy or sandy impurities present in an ore are called gangue (or matrix). Flux is added during smelting to react with these impurities, and the resulting fused mass is called slag, which is lighter and floats on top of the molten metal for easy removal.
This question belongs to: Science chemistry
Question #623
In the extraction of iron, limestone is added as a flux to remove:
A. Silica (sand)
B. Iron oxide
C. Alumina
D. Copper sulfide
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Correct Answer: Option A

Explanation:
In a blast furnace, limestone (CaCO₃) decomposes to CaO, which acts as a basic flux. It reacts with the acidic impurity silica (SiO₂) to form calcium silicate slag (CaSiO₃), which is lighter and floats on top of the molten iron, allowing it to be separated and removed.
This question belongs to: Science chemistry
Question #624
Assertion (A): Silver and gold occur in the free state in nature. Reason (R): They are highly reactive metals.
A. A is true but R is false.
B. Both A and R are true but R is NOT the correct explanation of A.
C. Both A and R are true and R is the correct explanation of A.
D. A is false but R is true.
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Correct Answer: Option A

Explanation:
Silver and gold are noble metals and occur in the free (native) state in nature because they are extremely unreactive (least reactive), not highly reactive. They do not readily combine with oxygen, moisture, or acids. Thus, A is true, but R is false.
This question belongs to: Science chemistry
Question #625
Which of the following is a nitrogenous fertilizer?
A. Gypsum
B. Muriate of potash
C. Superphosphate
D. Urea
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Correct Answer: Option D

Explanation:
Urea (CO(NH₂)₂) is a nitrogenous fertilizer with the highest nitrogen content (about 46%). Superphosphate provides phosphorus, muriate of potash (KCl) provides potassium, and gypsum (CaSO₄·2H₂O) is a soil conditioner providing calcium and sulfur, not primary NPK nutrients.
This question belongs to: Science chemistry
Question #626
DAP stands for:
A. Diammonium Phosphate
B. Diatomic Potassium
C. Diatomic Phosphorus
D. Diammonium Phosphide
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Correct Answer: Option A

Explanation:
DAP stands for Diammonium Phosphate, with the chemical formula (NH₄)₂HPO₄. It is a widely used phosphorus fertilizer that also supplies nitrogen. It is highly soluble and quickly releases nutrients into the soil, making it popular for starter fertilizers in agriculture.
This question belongs to: Science chemistry
Question #627
Which of the following is an example of a biofertilizer?
A. Ammonium sulfate
B. Urea
C. NPK
D. Rhizobium
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Correct Answer: Option D

Explanation:
Biofertilizers are living microorganisms that enrich the soil quality. Rhizobium is a symbiotic bacterium found in the root nodules of leguminous plants that fixes atmospheric nitrogen. Urea, NPK, and ammonium sulfate are chemical fertilizers synthesized through industrial processes.
This question belongs to: Science chemistry
Question #628
NPK fertilizers provide which three primary macronutrients to plants?
A. Nitrogen, Phosphorus, Calcium
B. Nitrogen, Potassium, Carbon
C. Nickel, Phosphorus, Potassium
D. Nitrogen, Phosphorus, Potassium
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Correct Answer: Option D

Explanation:
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K). These are the three primary macronutrients essential for plant growth. N promotes leafy growth, P aids root and flower development, and K improves overall health and disease resistance in crops.
This question belongs to: Science chemistry
Question #629
Excessive use of chemical fertilizers can lead to:
A. Improvement of soil texture.
B. Increase in beneficial soil microbes.
C. Eutrophication of water bodies.
D. Increased soil fertility indefinitely.
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Correct Answer: Option C

Explanation:
Excessive use of chemical fertilizers, especially those containing nitrogen and phosphorus, can lead to runoff into water bodies. This causes eutrophication (algal blooms), which depletes oxygen in the water and kills aquatic life. It also degrades soil health and kills beneficial microbes over time.
This question belongs to: Science chemistry
Question #630
Which bacterium is used as a biofertilizer for fixing atmospheric nitrogen in non-leguminous crops?
A. Nitrosomonas
B. Rhizobium
C. Azotobacter
D. Nitrobacter
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Correct Answer: Option C

Explanation:
Azotobacter is a free-living aerobic bacterium that fixes atmospheric nitrogen in the soil, making it available to non-leguminous crops. Rhizobium is symbiotic and specific to legumes. Nitrobacter and Nitrosomonas are involved in nitrification (converting ammonia to nitrites/nitrates), not nitrogen fixation.
This question belongs to: Science chemistry
Question #631
The chemical formula of urea is:
A. (NH₄)₂SO₄
B. NH₄NO₃
C. Ca(H₂PO₄)₂
D. CO(NH₂)₂
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Correct Answer: Option D

Explanation:
Urea is chemically carbamide, with the formula CO(NH₂)₂. It is synthesized from ammonia and carbon dioxide in the Bosch-Meiser process. Option A is ammonium nitrate, B is ammonium sulfate, and D is calcium dihydrogen phosphate (a component of single superphosphate).
This question belongs to: Science chemistry
Question #632
Assertion (A): Leguminous plants do not require nitrogenous fertilizers. Reason (R): They have Rhizobium bacteria in their root nodules that fix atmospheric nitrogen.
A. Both A and R are true but R is NOT the correct explanation of A.
B. Both A and R are true and R is the correct explanation of A.
C. A is false but R is true.
D. A is true but R is false.
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Correct Answer: Option B

Explanation:
Leguminous plants (like peas, beans) have a symbiotic relationship with Rhizobium bacteria in their root nodules. These bacteria convert atmospheric N₂ into usable nitrogen compounds, fulfilling the plant's nitrogen needs. Thus, they generally do not need external nitrogenous fertilizers. Both statements are correct and R explains A.
This question belongs to: Science chemistry
Question #633
The chemical name of washing soda is:
A. Sodium hydroxide
B. Sodium bicarbonate
C. Sodium chloride
D. Sodium carbonate decahydrate
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Correct Answer: Option D

Explanation:
Washing soda is sodium carbonate decahydrate, with the chemical formula Na₂CO₃·10H₂O. Sodium bicarbonate is baking soda (NaHCO₃). Sodium hydroxide is caustic soda (NaOH), and sodium chloride is common table salt (NaCl). Washing soda is used for cleaning and water softening.
This question belongs to: Science chemistry
Question #634
Which acid is known as the 'King of Chemicals'?
A. Nitric acid
B. Acetic acid
C. Sulphuric acid
D. Hydrochloric acid
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Correct Answer: Option C

Explanation:
Sulphuric acid (H₂SO₄) is known as the 'King of Chemicals' because of its extensive use in various industries, including fertilizers, dyes, detergents, and petroleum refining. Its production is often considered an indicator of a country's industrial strength and economic development.
This question belongs to: Science chemistry
Question #635
The process used for the manufacture of ammonia is:
A. Haber's process
B. Solvay process
C. Ostwald's process
D. Contact process
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Correct Answer: Option A

Explanation:
Ammonia (NH₃) is manufactured by the Haber process, which involves the direct combination of nitrogen and hydrogen gases at high pressure (200 atm) and moderate temperature (450°C) in the presence of an iron catalyst. The Contact process is for sulfuric acid, and Ostwald's is for nitric acid.
This question belongs to: Science chemistry
Question #636
Hydrogen peroxide (H₂O₂) is commonly used as a:
A. Refrigerant
B. Fuel
C. Mild antiseptic and bleaching agent
D. Fertilizer
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Correct Answer: Option C

Explanation:
Hydrogen peroxide is a strong oxidizing agent. In dilute solutions (3-6%), it is used as a mild antiseptic for minor cuts and as a bleaching agent for hair, teeth, and delicate materials like silk and wool. It decomposes into water and oxygen.
This question belongs to: Science chemistry
Question #637
The chemical formula of nitric acid is:
A. H₃PO₄
B. HNO₃
C. H₂SO₄
D. HCl
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Correct Answer: Option B

Explanation:
Nitric acid is a strong mineral acid with the chemical formula HNO₃. It is also known as aqua fortis. HCl is hydrochloric acid, H₂SO₄ is sulfuric acid, and H₃PO₄ is phosphoric acid. Nitric acid is widely used in fertilizers and explosives.
This question belongs to: Science chemistry
Question #638
Which of the following is used as a drying agent (dehydrating agent)?
A. Concentrated H₂SO₄
B. Aqueous NaOH
C. Dilute HCl
D. Dilute HNO₃
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Correct Answer: Option A

Explanation:
Concentrated sulfuric acid (H₂SO₄) has a very strong affinity for water and is widely used as a dehydrating agent in laboratories. It can remove water molecules from compounds, such as converting sugar (carbohydrate) to carbon, and is used to dry gases that do not react with it.
This question belongs to: Science chemistry
Question #639
Ethanol is chemically:
A. CH₃COOH
B. C₂H₅OH
C. C₂H₅COOH
D. CH₃OH
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Correct Answer: Option B

Explanation:
Ethanol, commonly known as ethyl alcohol, has the chemical formula C₂H₅OH. Methanol is CH₃OH. Acetic acid (ethanoic acid) is CH₃COOH, and propionic acid is C₂H₅COOH. Ethanol is widely used as a solvent, in alcoholic beverages, and as a biofuel.
This question belongs to: Science chemistry
Question #640
The Ostwald process is used for the manufacture of:
A. Sulphuric acid
B. Sodium carbonate
C. Ammonia
D. Nitric acid
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Correct Answer: Option D

Explanation:
The Ostwald process is the industrial method for manufacturing nitric acid (HNO₃). It involves the catalytic oxidation of ammonia (NH₃) to nitric oxide (NO), which is then further oxidized to nitrogen dioxide (NO₂) and absorbed in water to form concentrated nitric acid.
This question belongs to: Science chemistry

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