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 #881
The valency of iron in Fe₂O₃ is:
A. 3
B. 2
C. 4
D. 1
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Correct Answer: Option A

Explanation:
In Fe₂O₃, oxygen has valency 2. Two Fe atoms combined with three O atoms: total negative charge = 6. For two Fe, total positive = 6, so each Fe has +3. Valency = 3 (ferric). In FeO, valency is 2 (ferrous).
This question belongs to: Science chemistry
Question #882
Which of the following elements has the highest electronegativity?
A. Oxygen
B. Nitrogen
C. Chlorine
D. Fluorine
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Correct Answer: Option D

Explanation:
Fluorine is the most electronegative element (Pauling scale 3.98). Electronegativity increases across a period and decreases down a group. Hence F > O > Cl > N.
This question belongs to: Science chemistry
Question #883
The reaction between magnesium and dilute hydrochloric acid produces:
A. MgCl₂ and O₂
B. MgCl₂ and H₂
C. MgO and Cl₂
D. MgO and H₂O
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Correct Answer: Option B

Explanation:
Mg + 2HCl → MgCl₂ + H₂↑. Magnesium displaces hydrogen from acid. This is a single displacement and redox reaction. Copper does not react similarly.
This question belongs to: Science chemistry
Question #884
An indicator that remains colorless in acid and turns pink in base is:
A. Phenolphthalein
B. Litmus
C. Turmeric
D. Methyl orange
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Correct Answer: Option A

Explanation:
Phenolphthalein: pH range 8.3–10; colorless below 8.3, pink above. Litmus is red in acid, blue in base. Methyl orange red in acid, yellow in base. Turmeric yellow in acid, reddish-brown in base.
This question belongs to: Science chemistry
Question #885
Baking powder is a mixture of:
A. NaHCO₃ and NaCl
B. Na₂CO₃ and HCl
C. NaHCO₃ and tartaric acid
D. NaHCO₃ and acetic acid
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Correct Answer: Option C

Explanation:
Baking powder = sodium bicarbonate + weak solid acid (usually tartaric acid or cream of tartar). On moistening, they react to produce CO₂, causing dough to rise without requiring external acidic ingredient.
This question belongs to: Science chemistry
Question #886
Which of the following metals is used in the thermite welding process?
A. Zinc
B. Copper
C. Lead
D. Aluminium
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Correct Answer: Option D

Explanation:
Thermite: Fe₂O₃ + 2Al → 2Fe + Al₂O₃. Aluminium powder reduces iron oxide, producing molten iron for welding. Al is chosen due to its high reactivity and exothermic reaction.
This question belongs to: Science chemistry
Question #887
The structure of diamond is:
A. Linear chain
B. Layered hexagonal
C. Cubic close-packed
D. Tetrahedral network
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Correct Answer: Option D

Explanation:
Each carbon in diamond is sp³ hybridized and covalently bonded to four others in a tetrahedral geometry, forming a rigid 3D network. Graphite has a layered structure.
This question belongs to: Science chemistry
Question #888
Ethene undergoes which type of reaction with bromine water?
A. Addition
B. Dehydration
C. Oxidation
D. Substitution
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Correct Answer: Option A

Explanation:
Ethene (C₂H₄) adds Br₂ across the double bond to form 1,2-dibromoethane. Bromine water decolorizes, a test for unsaturation. Alkanes undergo substitution.
This question belongs to: Science chemistry
Question #889
The fuel with the highest cetane number is:
A. Diesel
B. Methane
C. Kerosene
D. Petrol
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Correct Answer: Option A

Explanation:
Cetane number measures ignition quality of diesel fuel; higher cetane means easier ignition. Diesel has high cetane (40-55). Petrol has octane number. Methane is gas.
This question belongs to: Science chemistry
Question #890
In an electrochemical cell, the salt bridge provides:
A. Ionic contact and completes the circuit
B. Voltage
C. Electron flow
D. Current
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Correct Answer: Option A

Explanation:
The salt bridge (often KCl-agar) allows ion migration to maintain electrical neutrality in half-cells, completing the circuit. It prevents direct mixing of electrolytes.
This question belongs to: Science chemistry
Question #891
According to Boyle's law, the product of pressure and volume for a fixed mass of gas at constant temperature is:
A. Constant
B. Depends on gas
C. Variable
D. Zero
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Correct Answer: Option A

Explanation:
PV = constant at constant T and n. This is Boyle's law. If either P or V changes, the other changes inversely.
This question belongs to: Science chemistry
Question #892
Graham's law is applicable to:
A. Gases
B. All states
C. Liquids
D. Solids
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Correct Answer: Option A

Explanation:
Graham's law of effusion/diffusion applies to gases. It states that rate is inversely proportional to square root of molar mass. It is used to separate isotopes.
This question belongs to: Science chemistry
Question #893
The catalyst used in the Ostwald process for nitric acid manufacture is:
A. Iron
B. Platinum-Rhodium gauze
C. Vanadium pentoxide
D. Nickel
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Correct Answer: Option B

Explanation:
Ostwald process: NH₃ oxidized to NO over Pt-Rh catalyst at 800°C. Fe for Haber; Ni for hydrogenation; V₂O₅ for SO₂ oxidation.
This question belongs to: Science chemistry
Question #894
The enzyme that hydrolyzes urea into ammonia and CO₂ is:
A. Urease
B. Zymase
C. Lipase
D. Pepsin
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Correct Answer: Option A

Explanation:
Urease catalyzes urea hydrolysis: (NH₂)₂CO + H₂O → 2NH₃ + CO₂. It is found in bacteria and plants. Used in clinical tests for urea.
This question belongs to: Science chemistry
Question #895
In the extraction of copper from copper pyrites, the ore is first concentrated by:
A. Froth flotation
B. Leaching
C. Magnetic separation
D. Calcination
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Correct Answer: Option A

Explanation:
Copper pyrites (CuFeS₂) is a sulfide ore, concentrated by froth flotation using pine oil and water. Then roasting, smelting, and refining.
This question belongs to: Science chemistry
Question #896
The nutrient element essential for root development in plants is:
A. Nitrogen
B. Phosphorus
C. Calcium
D. Potassium
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Correct Answer: Option B

Explanation:
Phosphorus promotes strong root growth, flower and seed production. Nitrogen promotes leaf growth; potassium helps overall vigor and disease resistance.
This question belongs to: Science chemistry
Question #897
Which acid is called the 'King of Chemicals'?
A. Sulphuric acid
B. Hydrochloric acid
C. Phosphoric acid
D. Nitric acid
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Correct Answer: Option A

Explanation:
Sulphuric acid is used in the production of fertilizers, chemicals, petroleum refining, etc., earning the title. It's not the strongest acid but the most industrially important.
This question belongs to: Science chemistry
Question #898
Hydrogen peroxide is a:
A. Strong base
B. Reducing agent only
C. Strong acid
D. Bleaching and oxidizing agent
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Correct Answer: Option D

Explanation:
H₂O₂ acts as both oxidizing and reducing agent, but commonly used as a bleaching agent (oxidizing) and disinfectant. It is weakly acidic.
This question belongs to: Science chemistry
Question #899
Ethanol is produced by fermentation of sugar. The microorganisms used are:
A. Virus
B. Algae
C. Bacteria
D. Yeast
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Correct Answer: Option D

Explanation:
Yeast (Saccharomyces cerevisiae) enzymes convert glucose to ethanol and CO₂ anaerobically. Bacteria produce lactic acid or acetic acid; algae are photosynthetic.
This question belongs to: Science chemistry
Question #900
Synthetic detergents have advantage over soaps because:
A. They are natural products
B. They are biodegradable
C. They are cheaper
D. They work well in hard water
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Correct Answer: Option D

Explanation:
Detergents do not form scum with Ca²⁺/Mg²⁺, so they clean effectively in hard water. Soaps form insoluble precipitates. Biodegradability varies; some detergents are non-biodegradable.
This question belongs to: Science chemistry

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