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 #721
Which process is used to concentrate sulfide ores?
A. Froth flotation
B. Magnetic separation
C. Calcination
D. Leaching with NaOH
Discuss
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Correct Answer: Option A

Explanation:
Froth flotation separates sulfide ore particles from gangue by using oil and water. The ore particles adhere to the froth and float, while gangue sinks. Used for ZnS, PbS, CuFeS₂. Magnetic separation for magnetite, leaching for bauxite.
This question belongs to: Science chemistry
Question #722
Urea is a fertilizer that provides:
A. Only phosphorus
B. Only potassium
C. Nitrogen and phosphorus
D. Only nitrogen
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Correct Answer: Option D

Explanation:
Urea, CO(NH₂)₂, is a straight nitrogenous fertilizer with about 46% N. It contains no phosphorus or potassium. It is converted to ammonium carbonate in soil by urease enzyme, then to nitrates.
This question belongs to: Science chemistry
Question #723
Ammonium sulfate is a fertilizer that supplies:
A. Nitrogen only
B. Potassium and nitrogen
C. Nitrogen and sulfur
D. Phosphorus and sulfur
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Correct Answer: Option C

Explanation:
(NH₄)₂SO₄ contains 21% nitrogen and 24% sulfur. Both are plant nutrients. It is a straight nitrogenous fertilizer with sulfur as secondary nutrient. It is especially useful for sulfur-deficient soils.
This question belongs to: Science chemistry
Question #724
Sulphuric acid is called 'king of chemicals' because:
A. It is the strongest acid
B. It is found in nature
C. It is used in the manufacture of many other chemicals
D. It is the cheapest acid
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Correct Answer: Option C

Explanation:
H₂SO₄ is used in production of fertilizers, detergents, dyes, explosives, petroleum refining, and many other chemicals. Its wide industrial use earns it the title. It's not the strongest (e.g., HClO₄ is stronger).
This question belongs to: Science chemistry
Question #725
Nitric acid reacts with copper to produce:
A. Nitrogen and water
B. Hydrogen
C. Nitrogen dioxide and copper nitrate
D. Oxygen
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Correct Answer: Option C

Explanation:
Cu + 4HNO₃ (conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O. Dilute HNO₃ gives NO instead of NO₂. Copper does not produce H₂ with HNO₃ because HNO₃ is an oxidizing acid.
This question belongs to: Science chemistry
Question #726
Sodium hydroxide turns red litmus blue because it is:
A. Basic
B. Neutral
C. Salty
D. Acidic
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Correct Answer: Option A

Explanation:
NaOH is a strong base; it dissociates to give OH⁻ ions, making the solution basic (pH >7). Bases turn red litmus blue. Acids turn blue litmus red.
This question belongs to: Science chemistry
Question #727
Hydrogen peroxide decomposes slowly on exposure to light. To prevent this, it is stored in:
A. Metal containers
B. Dark colored bottles
C. Open beakers
D. Clear glass bottles
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Correct Answer: Option B

Explanation:
Light catalyzes decomposition of H₂O₂. Dark bottles (amber) block light, stabilizing it. Often a stabilizer like urea or phosphoric acid is added. Metal containers may catalyze decomposition.
This question belongs to: Science chemistry
Question #728
Methanol is toxic because it is metabolized to:
A. Acetone
B. Formaldehyde and formic acid
C. Acetic acid
D. Ethanol
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Correct Answer: Option B

Explanation:
In the liver, methanol is oxidized to formaldehyde, then to formic acid, which damages the optic nerve and can cause blindness or death. Ethanol is used as an antidote by competing for the enzyme alcohol dehydrogenase.
This question belongs to: Science chemistry
Question #729
Soap molecules form micelles in water. The hydrophilic part is:
A. The potassium ion
B. The carboxylate head
C. The hydrocarbon tail
D. The entire molecule
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Correct Answer: Option B

Explanation:
The head (–COO⁻) is ionic and attracted to water (hydrophilic). The long hydrocarbon tail is non-polar and hydrophobic, dissolving in grease. This amphiphilic nature allows cleaning.
This question belongs to: Science chemistry
Question #730
Which of the following is an example of a synthetic detergent?
A. Sodium stearate
B. Calcium oleate
C. Potassium palmitate
D. Sodium lauryl sulfate
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Correct Answer: Option D

Explanation:
Sodium lauryl sulfate (CH₃(CH₂)₁₁OSO₃Na) is a synthetic detergent with a sulfate group. Sodium stearate and potassium palmitate are soaps (carboxylate salts). Calcium oleate is soap scum.
This question belongs to: Science chemistry
Question #731
The raw materials for cement are:
A. Limestone and clay
B. Sand and soda ash
C. Gypsum and sand
D. Marble and salt
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Correct Answer: Option A

Explanation:
Portland cement is made by heating a mixture of limestone (CaCO₃) and clay (SiO₂, Al₂O₃, Fe₂O₃) in a kiln. The resulting clinker is ground with gypsum. Soda ash and sand are for glass.
This question belongs to: Science chemistry
Question #732
Which plastic is used for making electrical switches and handles of utensils?
A. PVC
B. Bakelite
C. Teflon
D. Polythene
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Correct Answer: Option B

Explanation:
Bakelite is a thermosetting plastic, heat resistant and electrical insulator. Polythene and PVC are thermoplastics; they soften on heating. Teflon is non-stick.
This question belongs to: Science chemistry
Question #733
Teflon is chemically inert because of:
A. Presence of strong C-F bonds
B. Its layered structure
C. Its ionic nature
D. Presence of double bonds
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Correct Answer: Option A

Explanation:
The carbon-fluorine bond is one of the strongest covalent bonds, making PTFE resistant to attack by chemicals and heat. The fluorine atoms also shield the carbon backbone.
This question belongs to: Science chemistry
Question #734
The monomer of PVC is:
A. Vinyl chloride
B. Ethene
C. Tetrafluoroethene
D. Styrene
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Correct Answer: Option A

Explanation:
PVC is polyvinyl chloride, made from vinyl chloride (CH₂=CHCl). Ethene gives polythene; tetrafluoroethene gives Teflon; styrene gives polystyrene.
This question belongs to: Science chemistry
Question #735
Permanent hardness of water is caused by:
A. Bicarbonates of Ca and Mg
B. Potassium sulfate
C. Sodium chloride
D. Chlorides and sulfates of Ca and Mg
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Correct Answer: Option D

Explanation:
Permanent hardness is due to CaCl₂, CaSO₄, MgCl₂, MgSO₄. These do not precipitate on boiling. Temporary hardness (bicarbonates) is removed by boiling. Both can be removed by ion exchange or washing soda.
This question belongs to: Science chemistry
Question #736
The method of purifying water by passing it through a semipermeable membrane under pressure is called:
A. Chlorination
B. Ozonation
C. Reverse osmosis
D. Distillation
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Correct Answer: Option C

Explanation:
Reverse osmosis (RO) uses pressure to force water through a membrane that blocks dissolved salts and impurities. Distillation uses boiling/condensation. Chlorination and ozonation are disinfection methods, not for desalination.
This question belongs to: Science chemistry
Question #737
Which of the following air pollutants is a primary cause of acid rain?
A. CO
B. CH₄
C. O₃
D. SO₂
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Correct Answer: Option D

Explanation:
SO₂ (from burning coal) and NOₓ dissolve in rain to form H₂SO₄ and HNO₃. CO is toxic but does not form strong acid; CH₄ is greenhouse gas; ground-level O₃ is secondary pollutant and irritant.
This question belongs to: Science chemistry
Question #738
The ozone layer absorbs:
A. Visible light
B. Infrared radiation
C. Ultraviolet radiation
D. Radio waves
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Correct Answer: Option C

Explanation:
Stratospheric ozone absorbs harmful UV-B and UV-C radiation from the sun, protecting living organisms. Depletion by CFCs increases UV at surface. Infrared is absorbed by greenhouse gases.
This question belongs to: Science chemistry
Question #739
Which of the following is an alpha particle?
A. Electron
B. Neutron
C. Helium nucleus
D. Proton
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Correct Answer: Option C

Explanation:
Alpha particle = ⁴₂He²⁺ (2 protons + 2 neutrons). Beta particle = electron or positron. Gamma = electromagnetic radiation. Alpha has low penetration, high ionization.
This question belongs to: Science chemistry
Question #740
The half-life of a radioactive sample is 2 hours. What fraction remains after 6 hours?
A. 1/16
B. 1/4
C. 1/2
D. 1/8
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Correct Answer: Option D

Explanation:
Number of half-lives = 6/2 = 3. Remaining = (1/2)³ = 1/8. After each half-life, half the remaining decays.
This question belongs to: Science chemistry

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