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 21 of 55
Question #401
Which of the following elements is a metalloid?
A. Germanium
B. Aluminium
C. Chlorine
D. Sodium
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Correct Answer: Option A

Explanation:
Germanium (Ge) is a metalloid, exhibiting properties of both metals and non-metals. It is a semiconductor used in transistors. Sodium and aluminium are metals. Chlorine is a non-metal. Metalloids are located along the zigzag line in the p-block.
This question belongs to: Science chemistry
Question #402
Which property decreases down a group in the periodic table?
A. Metallic character
B. Atomic radius
C. Number of shells
D. Ionization energy
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Correct Answer: Option D

Explanation:
Ionization energy decreases down a group because atomic size increases, and the outermost electron is farther from the nucleus with increased shielding, making it easier to remove. Atomic radius increases, metallic character increases, and number of shells increases down a group.
This question belongs to: Science chemistry
Question #403
In the reaction 2SO₂ + O₂ → 2SO₃, the type of reaction is:
A. Combination
B. Neutralization
C. Displacement
D. Decomposition
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Correct Answer: Option A

Explanation:
Two or more substances (SO₂ and O₂) combine to form a single product (SO₃). This is a combination reaction. It is also a redox reaction and is catalyzed by V₂O₅ in the Contact process for sulfuric acid. Decomposition is the opposite (breaking down). Displacement involves replacement of an element.
This question belongs to: Science chemistry
Question #404
Thermal decomposition of limestone produces:
A. Ca(OH)₂ and CO₂
B. CaO and CO
C. Ca and CO₂
D. CaO and CO₂
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Correct Answer: Option D

Explanation:
Limestone is CaCO₃. On strong heating, it decomposes to calcium oxide (quicklime) and carbon dioxide: CaCO₃ → CaO + CO₂. This is a decomposition reaction used in cement and lime manufacturing. CaO is used in building and as a drying agent.
This question belongs to: Science chemistry
Question #405
Which metal can displace iron from iron(II) sulfate solution?
A. Copper
B. Silver
C. Mercury
D. Zinc
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Correct Answer: Option D

Explanation:
Zinc is more reactive than iron (above in the reactivity series), so it can displace iron: Zn + FeSO₄ → ZnSO₄ + Fe. Silver, copper, and mercury are less reactive than iron and cannot displace it. The reactivity series predicts displacement: a more reactive metal displaces a less reactive one.
This question belongs to: Science chemistry
Question #406
Which of the following reactions is an oxidation-reduction reaction?
A. H₂ + Cl₂ → 2HCl
B. NaCl + AgNO₃ → AgCl + NaNO₃
C. NaOH + HCl → NaCl + H₂O
D. CaCO₃ → CaO + CO₂
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Correct Answer: Option A

Explanation:
In H₂ + Cl₂ → 2HCl, hydrogen is oxidized (0 to +1) and chlorine is reduced (0 to -1). Thus it's a redox reaction. The others: A and C are double displacement with no oxidation state change; D is decomposition with no change (Ca +2, C +4, O -2 throughout).
This question belongs to: Science chemistry
Question #407
The pH of a solution that turns red litmus blue is most likely:
A. 6
B. 11
C. 7
D. 3
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Correct Answer: Option B

Explanation:
Red litmus turning blue indicates a basic solution, pH > 7. pH 11 is strongly basic. pH 3 and 6 are acidic (blue litmus turns red). pH 7 is neutral (litmus remains purple). Litmus is a common natural indicator.
This question belongs to: Science chemistry
Question #408
Which salt is formed when hydrochloric acid reacts with sodium hydroxide?
A. Sodium carbonate
B. Sodium nitrate
C. Sodium sulfate
D. Sodium chloride
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Correct Answer: Option D

Explanation:
HCl + NaOH → NaCl + H₂O. This is a neutralization reaction producing sodium chloride (common salt). NaNO₃ from HNO₃, Na₂SO₄ from H₂SO₄, Na₂CO₃ from H₂CO₃ (weak acid).
This question belongs to: Science chemistry
Question #409
Baking powder contains baking soda and:
A. Magnesium sulfate
B. Sodium chloride
C. Calcium carbonate
D. Tartaric acid
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Correct Answer: Option D

Explanation:
Baking powder is a mixture of sodium bicarbonate (baking soda) and a mild edible acid, usually tartaric acid. When moistened and heated, they react to release CO₂, causing dough to rise. Baking soda alone requires an external acidic ingredient. The acid ensures complete reaction and avoids a bitter taste.
This question belongs to: Science chemistry
Question #410
The formula of bleaching powder is:
A. CaO
B. CaOCl₂
C. CaCl₂
D. CaCO₃
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Correct Answer: Option B

Explanation:
Bleaching powder is calcium oxychloride, CaOCl₂. It is produced by passing chlorine over dry slaked lime: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O. It is a mixed salt of Ca²⁺, Cl⁻, and OCl⁻ ions. It is used for bleaching and disinfection.
This question belongs to: Science chemistry
Question #411
Plaster of Paris hardens on mixing with water due to formation of:
A. CaSO₄·½H₂O
B. CaSO₄·2H₂O
C. CaO
D. CaSO₄
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Correct Answer: Option B

Explanation:
Plaster of Paris (CaSO₄·½H₂O) reacts with water to form gypsum (CaSO₄·2H₂O) which sets into a hard solid mass with slight expansion. Reaction: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O. This property is used for casting and setting broken bones.
This question belongs to: Science chemistry
Question #412
Which of the following metals is liquid at room temperature?
A. Mercury
B. Sodium
C. Aluminium
D. Zinc
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Correct Answer: Option A

Explanation:
Mercury (Hg) is the only metal that is liquid at room temperature. Gallium and cesium melt slightly above room temperature. Sodium is solid but soft. Zinc and aluminium are solids. Mercury is used in thermometers and barometers.
This question belongs to: Science chemistry
Question #413
The reactivity series lists metals in the order of:
A. Decreasing tendency to lose electrons
B. Increasing density
C. Increasing atomic mass
D. Decreasing reactivity
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Correct Answer: Option D

Explanation:
The reactivity series arranges metals from most reactive (K) to least reactive (Au). A metal higher in the series can displace a lower one from its salt solution. The order is based on tendency to lose electrons (form positive ions). More reactive = more electropositive.
This question belongs to: Science chemistry
Question #414
Rusting of iron is accelerated in:
A. Pure water without air
B. Dry air
C. Saline water
D. Vacuum
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Correct Answer: Option C

Explanation:
Saline water (containing NaCl) increases the electrical conductivity of the water, accelerating the electrochemical process of rusting. This is why ships and coastal structures rust faster. Dry air and vacuum have no moisture; pure water without dissolved oxygen slows rusting.
This question belongs to: Science chemistry
Question #415
Galvanization is coating iron with:
A. Chromium
B. Zinc
C. Tin
D. Nickel
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Correct Answer: Option B

Explanation:
Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting. Zinc acts as a sacrificial anode (more reactive than iron), corroding in preference to the iron even if the coating is scratched. Tin coating (tin-plating) protects only if the layer remains intact.
This question belongs to: Science chemistry
Question #416
Which allotrope of carbon is used in pencils?
A. Charcoal
B. Graphite
C. Fullerene
D. Diamond
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Correct Answer: Option B

Explanation:
Pencil 'lead' is a mixture of graphite and clay. Graphite's layered structure allows it to leave marks on paper. Diamond is too hard and would tear paper. Fullerene is a nanomaterial, not for writing. Charcoal is used for drawing but not pencils.
This question belongs to: Science chemistry
Question #417
Methane reacts with chlorine in the presence of sunlight to give:
A. Carbon tetrachloride
B. Ethane
C. Methyl chloride and HCl
D. Methanol
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Correct Answer: Option C

Explanation:
Methane undergoes substitution reaction with chlorine in UV light: CH₄ + Cl₂ → CH₃Cl + HCl. Further substitution can give CH₂Cl₂, CHCl₃, CCl₄. This is a free radical mechanism. It does not produce methanol or ethane.
This question belongs to: Science chemistry
Question #418
Petroleum is a mixture of:
A. Only alkenes
B. Hydrocarbons of various molecular weights
C. Only alkanes
D. Only aromatics
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Correct Answer: Option B

Explanation:
Petroleum (crude oil) is a complex mixture of hydrocarbons including alkanes, cycloalkanes, aromatics, and smaller amounts of other compounds containing sulfur, nitrogen, oxygen. It is separated into fractions by fractional distillation.
This question belongs to: Science chemistry
Question #419
CNG is considered a cleaner fuel than diesel because:
A. It is more expensive
B. It contains more carbon
C. It is a liquid
D. It produces less CO₂ and negligible particulate matter
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Correct Answer: Option D

Explanation:
CNG (mainly methane) has a higher H/C ratio than diesel, so it emits less CO₂ per unit energy. It burns almost completely, producing very little carbon monoxide, unburnt hydrocarbons, and particulate matter (soot). It also contains negligible sulfur, thus no SO₂ emissions.
This question belongs to: Science chemistry
Question #420
The calorific value of hydrogen is about:
A. 50 kJ/g
B. 150 kJ/g
C. 1000 kJ/g
D. 30 kJ/g
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Correct Answer: Option B

Explanation:
Hydrogen has a very high calorific value of about 141.9 kJ/g (higher heating value) or ~150 kJ/g approximate. This makes it an excellent fuel, though storage is challenging. Methane ~55 kJ/g, petrol ~47 kJ/g. Hydrogen fuel cells use it efficiently.
This question belongs to: Science chemistry

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