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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Page 46 of 55
Question #901
The main constituent of cement is:
A. Calcium carbonate
B. Magnesium oxide
C. Silica only
D. Calcium silicate
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Correct Answer: Option D

Explanation:
Portland cement primarily consists of calcium silicates (C₃S and C₂S) along with aluminates. These are formed by heating limestone and clay.
This question belongs to: Science chemistry
Question #902
Which plastic is used for making electrical insulation and pipes?
A. PVC
B. Polystyrene
C. Bakelite
D. Nylon
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Correct Answer: Option A

Explanation:
PVC is a good electrical insulator, resistant to chemicals and moisture, used for pipes, cable sheathing. Bakelite for switches; polystyrene for packaging.
This question belongs to: Science chemistry
Question #903
Vulcanization of rubber was discovered by:
A. John Boyd Dunlop
B. Wallace Carothers
C. Charles Goodyear
D. Leo Baekeland
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Correct Answer: Option C

Explanation:
Charles Goodyear accidentally discovered vulcanization (heating rubber with sulfur) in 1839, which improved rubber's elasticity and strength. Dunlop invented pneumatic tire; Baekeland invented Bakelite; Carothers nylon.
This question belongs to: Science chemistry
Question #904
Which of the following is a method to remove permanent hardness of water?
A. Adding washing soda
B. Cooling
C. Filtration
D. Boiling
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Correct Answer: Option A

Explanation:
Permanent hardness (due to CaSO₄ etc.) can be removed by adding Na₂CO₃, which precipitates CaCO₃. Boiling only removes temporary hardness. Ion exchange and calgon also work.
This question belongs to: Science chemistry
Question #905
Chlorine used in water purification acts by:
A. Dissolving salts
B. Removing suspended particles
C. Adding flavor
D. Killing microorganisms by oxidation
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Correct Answer: Option D

Explanation:
Chlorine forms hypochlorous acid (HOCl) which is a strong oxidizing agent that destroys bacteria and viruses. It does not remove particles (filtration does) or dissolved salts.
This question belongs to: Science chemistry
Question #906
Global warming is mainly caused by increase in atmospheric:
A. Carbon dioxide
B. Oxygen
C. Nitrogen
D. Argon
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Correct Answer: Option A

Explanation:
CO₂ levels have risen due to burning fossil fuels, enhancing greenhouse effect. Methane, N₂O also contribute. Nitrogen and oxygen are not greenhouse gases.
This question belongs to: Science chemistry
Question #907
Alpha rays are:
A. Electrons
B. Helium nuclei
C. Neutrons
D. Electromagnetic waves
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Correct Answer: Option B

Explanation:
Alpha rays consist of ⁴₂He²⁺ particles (2 protons + 2 neutrons). They have low penetration but high ionization power.
This question belongs to: Science chemistry
Question #908
Half-life of a radioactive isotope is 5 years. What percentage remains after 15 years?
A. 6.25%
B. 25%
C. 50%
D. 12.5%
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Correct Answer: Option D

Explanation:
15/5 = 3 half-lives. Remaining = (1/2)³ = 1/8 = 12.5%. Each half-life reduces the amount by half.
This question belongs to: Science chemistry
Question #909
The discovery of the electron was done by:
A. James Chadwick
B. Ernest Rutherford
C. J. J. Thomson
D. Niels Bohr
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Correct Answer: Option C

Explanation:
J.J. Thomson discovered the electron in 1897 using cathode ray tubes and determined its e/m ratio. Rutherford discovered the nucleus; Chadwick discovered neutron; Bohr proposed quantized model.
This question belongs to: Science chemistry
Question #910
Which of the following statements is correct regarding the modern periodic table?
A. Elements in a group have same number of valence electrons.
B. Noble gases are in Group 1.
C. It is based on atomic mass.
D. There are 8 periods.
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Correct Answer: Option A

Explanation:
Groups (vertical columns) contain elements with the same number of valence electrons, leading to similar chemical properties. The modern table is based on atomic number; 7 periods exist; noble gases are in Group 18.
This question belongs to: Science chemistry
Question #911
A mixture of sand and iodine can be separated by:
A. Filtration
B. Distillation
C. Sublimation
D. Magnetic separation
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Correct Answer: Option C

Explanation:
Iodine sublimes on heating, converting to vapor, leaving sand behind. Iodine vapors can be condensed. Filtration cannot separate two solids; distillation for liquids.
This question belongs to: Science chemistry
Question #912
An atom of element X has 6 protons and 8 neutrons. Its mass number is:
A. 6
B. 8
C. 2
D. 14
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Correct Answer: Option D

Explanation:
Mass number = protons + neutrons = 6 + 8 = 14. This corresponds to carbon-14 isotope. Atomic number = 6 (carbon).
This question belongs to: Science chemistry
Question #913
The valency of carbon in CO₂ is:
A. 1
B. 2
C. 3
D. 4
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Correct Answer: Option D

Explanation:
Carbon forms two double bonds with two oxygen atoms, sharing 4 electrons in total. Thus covalency = 4. Each oxygen has valency 2.
This question belongs to: Science chemistry
Question #914
Which of the following compounds has a coordinate bond?
A. NH₃
B. H₂O
C. CH₄
D. O₃
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Correct Answer: Option D

Explanation:
Ozone (O₃) has one coordinate bond; a central oxygen donates a lone pair to another oxygen. CH₄, NH₃, H₂O have ordinary covalent bonds, though NH₃ can donate a pair to form NH₄⁺.
This question belongs to: Science chemistry
Question #915
The force holding ions together in an ionic crystal is:
A. Hydrogen bond
B. Electrostatic attraction
C. Van der Waals
D. Covalent bond
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Correct Answer: Option B

Explanation:
Ionic compounds consist of oppositely charged ions held together by strong electrostatic forces (ionic bonds). This results in high melting points and solubility in polar solvents.
This question belongs to: Science chemistry
Question #916
Mendeleev's periodic table had anomalies because he arranged elements by:
A. Atomic mass
B. Electronegativity
C. Density
D. Atomic number
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Correct Answer: Option A

Explanation:
Mendeleev used atomic mass as basis. Anomalies like Ar (mass 40) placed before K (mass 39) occurred. These were resolved when Moseley proposed atomic number as the basis.
This question belongs to: Science chemistry
Question #917
Which property increases down a group?
A. Electron affinity
B. Electronegativity
C. Atomic radius
D. Ionization energy
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Correct Answer: Option C

Explanation:
Atomic radius increases down a group due to addition of new shells. Ionization energy, electronegativity, and electron affinity (generally) decrease down a group.
This question belongs to: Science chemistry
Question #918
The reaction CaO + H₂O → Ca(OH)₂ is a:
A. Combination
B. Displacement
C. Redox
D. Decomposition
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Correct Answer: Option A

Explanation:
Two reactants combine to form a single product, so combination (also called synthesis). No oxidation state change, so not redox. Decomposition is opposite.
This question belongs to: Science chemistry
Question #919
In the reaction 2Mg + O₂ → 2MgO, magnesium is:
A. Reduced
B. Precipitated
C. Decomposed
D. Oxidized
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Correct Answer: Option D

Explanation:
Mg goes from 0 to +2 oxidation state, losing electrons – oxidized. Oxygen is reduced (0 to -2). This is a combustion/combination redox reaction.
This question belongs to: Science chemistry
Question #920
A solution turns blue litmus red. The solution is:
A. Neutral
B. Acidic
C. Saline
D. Basic
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Correct Answer: Option B

Explanation:
Acids turn blue litmus red; bases turn red litmus blue. Litmus is a natural indicator from lichens, purple in neutral solution.
This question belongs to: Science chemistry

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