Chemistry MCQs

Question #281

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Who developed the modern periodic table based on atomic numbers?

A. John Newlands

B. Henry Moseley

C. Lothar Meyer

D. Dmitri Mendeleev

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Correct Answer: Option B

Explanation:
Henry Moseley established that the properties of elements are periodic functions of their atomic numbers, not atomic masses. This refined Mendeleev's table and resolved anomalies like Ar-K. The modern periodic table is thus based on Moseley's work. Mendeleev proposed the original table based on atomic masses. Newlands gave Law of Octaves. Meyer plotted atomic volume curve.

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Question #282

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Which of the following scientists is known for the discovery of the proton?

A. Eugen Goldstein

B. James Chadwick

C. Ernest Rutherford

D. J. J. Thomson

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Correct Answer: Option C

Explanation:
Ernest Rutherford is generally credited with the discovery of the proton in 1919 through the nuclear reaction: ¹⁴N + α particle → ¹⁷O + proton. Eugen Goldstein earlier observed canal rays (positive rays) which were later identified as protons by Rutherford. Thomson discovered electron, Chadwick neutron. So Rutherford is the accepted discoverer.

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Question #283

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The force that holds nucleons together in the nucleus is:

A. Strong nuclear force

B. Van der Waals force

C. Electrostatic force

D. Gravitational force

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Correct Answer: Option A

Explanation:
The strong nuclear force is the attractive force that binds protons and neutrons (nucleons) together in the nucleus, overcoming the electrostatic repulsion between protons. It is short-range and charge-independent. Electrostatic repulsion would otherwise blow the nucleus apart. Gravitational force is negligible at this scale. Van der Waals forces operate between molecules.

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Question #284

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The element with electronic configuration 2,8,6 belongs to:

A. Group 16, Period 3

B. Group 16, Period 2

C. Group 18, Period 3

D. Group 6, Period 3

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Correct Answer: Option A

Explanation:
Total electrons = 16 (Sulfur). Period = number of shells = 3. Valence electrons = 6, group = 10+6 = 16 (Group 16, chalcogens). Group 6 would be 6 valence electrons but in d-block, not applicable. Group 18 has 8 valence electrons (except He). So sulfur is in group 16, period 3.

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Question #285

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The element with the largest atomic radius in period 3 is:

A. Mg

B. Cl

C. Na

D. Ar

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Correct Answer: Option C

Explanation:
Atomic radius decreases across a period due to increasing nuclear charge. Sodium (Na) is the first element in period 3, thus it has the largest atomic radius. Argon (noble gas) has the smallest (though noble gas radii are van der Waals and larger than covalent, but still trend is decreasing). For metals, Na > Mg > Al; non-metals further smaller.

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Question #286

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Which of the following is a combination reaction?

A. NaOH + HCl → NaCl + H₂O

B. CaCO₃ → CaO + CO₂

C. 2H₂ + O₂ → 2H₂O

D. Fe + CuSO₄ → FeSO₄ + Cu

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Correct Answer: Option C

Explanation:
2H₂ + O₂ → 2H₂O is a combination reaction where two or more reactants combine to form a single product. A is decomposition. C is displacement. D is neutralization (also double displacement). Combination reactions are generally exothermic. Another example: C + O₂ → CO₂.

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Question #287

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In the reaction Fe₂O₃ + 2Al → Al₂O₃ + 2Fe, which element is oxidized?

A. Fe

B. None

C. Al

D. O

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Correct Answer: Option C

Explanation:
Aluminium goes from 0 to +3 oxidation state (Al → Al³⁺ + 3e⁻), so it is oxidized. Iron goes from +3 to 0 (Fe³⁺ + 3e⁻ → Fe), reduced. This is a thermite reaction, highly exothermic, used for welding. Al is the reducing agent, Fe₂O₃ is the oxidizing agent. Oxidation is loss of electrons.

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Question #288

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Which of the following indicators is synthetic?

A. Red cabbage juice

B. Phenolphthalein

C. Litmus

D. Turmeric

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Correct Answer: Option B

Explanation:
Phenolphthalein is a synthetic acid-base indicator, organic compound prepared in the lab. Litmus is a natural dye from lichens. Turmeric is a natural indicator (yellow in acid, reddish brown in base). Red cabbage juice is natural. Synthetic indicators are often used in titrations: methyl orange, phenolphthalein.

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Question #289

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The pH of pure water at 25°C is 7. This is because:

A. It has no ions

B. It contains only OH⁻

C. It contains equal concentrations of H⁺ and OH⁻ ions

D. It is a strong acid

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Correct Answer: Option C

Explanation:
Water self-ionizes: H₂O ⇌ H⁺ + OH⁻. At 25°C, [H⁺] = [OH⁻] = 10⁻⁷ mol/L, so Kw = 10⁻¹⁴ and pH = pOH = 7. A solution is neutral when [H⁺] = [OH⁻]. pH 7 is neutral only at 25°C; at higher temperatures, Kw increases, pH of neutrality drops but still [H⁺]=[OH⁻].

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Question #290

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Which of the following is an acidic salt?

A. K₂SO₄

B. CaOCl₂

C. NaHCO₃

D. Na₂CO₃

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Correct Answer: Option C

Explanation:
Sodium bicarbonate (NaHCO₃) is an acidic salt because it contains a replaceable hydrogen atom (can neutralize bases). Its aqueous solution is mildly basic due to hydrolysis, but chemically it is an acid salt (formed by partial replacement of H of carbonic acid). K₂SO₄ is normal salt, CaOCl₂ is mixed salt, Na₂CO₃ is normal salt. Acid salts can react with bases.

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Question #291

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The metal used in the manufacture of stainless steel is:

A. Copper

B. Zinc

C. Chromium

D. Lead

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Correct Answer: Option C

Explanation:
Stainless steel is an iron alloy containing at least 10.5% chromium, which provides corrosion resistance by forming a passive chromium oxide layer. Nickel and molybdenum may also be added. Copper and zinc are components of brass. Lead is used in batteries and solder. Chromium is essential for 'stainless' property.

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Question #292

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Which of the following is a saturated carbon compound?

A. C₂H₂

B. C₂H₄

C. C₃H₆

D. C₄H₁₀

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Correct Answer: Option D

Explanation:
C₄H₁₀ (butane) follows CnH₂n+2, indicating no double or triple bonds, i.e., saturated alkane. C₂H₄ is ethene (alkene), C₃H₆ could be propene or cycloalkane (but alkene formula), C₂H₂ is ethyne (alkyne). Saturated hydrocarbons contain only single bonds and undergo substitution reactions.

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Question #293

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The major component of petroleum gas (associated gas) is:

A. Hydrogen

B. Propane

C. Methane

D. Butane

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Correct Answer: Option C

Explanation:
Petroleum gas, also known as natural gas associated with oil deposits, is primarily methane (CH₄) with smaller amounts of ethane, propane, and butane. LPG is propane and butane. Methane is the lightest hydrocarbon. It is separated and used as fuel (CNG) or petrochemical feedstock.

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Question #294

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Which of the following reactions is used to produce hydrogen for fuel cells?

A. Saponification

B. Electrolysis of water

C. Neutralization

D. Combustion of methane

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Correct Answer: Option B

Explanation:
Electrolysis of water produces pure hydrogen and oxygen: 2H₂O → 2H₂ + O₂. Hydrogen is used in fuel cells to generate electricity. It can also be produced by steam reforming of natural gas, but electrolysis yields clean hydrogen if powered by renewable energy. Combustion of methane produces energy, not hydrogen. Neutralization gives salt and water.

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Question #295

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In a galvanic cell, the anode is:

A. Negative electrode where oxidation occurs

B. Connected to cathode externally

C. Where reduction occurs

D. Positive electrode

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Correct Answer: Option A

Explanation:
In a galvanic (voltaic) cell, chemical energy converts to electrical energy. Oxidation occurs at the anode, which is the negative electrode (electrons leave from it). Reduction occurs at the cathode, which is positive. This is opposite to electrolytic cell where anode is positive. Daniell cell: Zn anode (-), Cu cathode (+).

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Question #296

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If the temperature of a gas is increased from 27°C to 327°C at constant pressure, the volume becomes how many times the original?

A. 2 times

B. 1.5 times

C. 4 times

D. 3 times

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Correct Answer: Option A

Explanation:
Use Charles' law: V₁/T₁ = V₂/T₂. T in Kelvin: T₁ = 27+273 = 300 K, T₂ = 327+273 = 600 K. V₂/V₁ = T₂/T₁ = 600/300 = 2. Volume doubles. The ratio is 2:1. Note that 27 to 327 is a 300°C increase, but absolute temperature doubles.

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Question #297

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Which of the following catalysts is used in the hydrogenation of alkenes?

A. V₂O₅

B. Pt or Ni

C. MnO₂

D. Fe

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Correct Answer: Option B

Explanation:
Hydrogenation of alkenes (addition of H₂ across double bond) is catalyzed by finely divided metals like nickel, platinum, or palladium. These adsorb H₂ and the unsaturated compound, facilitating reaction. V₂O₅ is for oxidation (Contact), MnO₂ for H₂O₂ decomposition, Fe for Haber process. Nickel is the most common industrial catalyst for hydrogenation.

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Question #298

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Which of the following is NOT a method of concentration of ore?

A. Froth flotation

B. Smelting

C. Magnetic separation

D. Leaching

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Correct Answer: Option B

Explanation:
Smelting is a reduction process, not concentration. Concentration (beneficiation) methods include gravity separation, magnetic separation, froth flotation, and leaching (chemical). Smelting involves heating concentrated ore with a reducing agent to extract metal. For example, hematite concentrated by washing, then smelted in blast furnace.

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Question #299

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Which of the following is a micronutrient for plants?

A. Potassium

B. Phosphorus

C. Zinc

D. Nitrogen

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Correct Answer: Option C

Explanation:
Zinc (Zn) is a micronutrient required in small amounts for plant growth, enzyme activation, and chlorophyll synthesis. Nitrogen, phosphorus, potassium are macronutrients (primary). Micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl. Deficiency of Zn causes stunted growth and chlorosis. Fertilizers often include micronutrients.

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Question #300

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The acid present in ant sting is:

A. Formic acid

B. Lactic acid

C. Acetic acid

D. Citric acid

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Correct Answer: Option A

Explanation:
Ant sting contains formic acid (methanoic acid, HCOOH), causing irritation. Nettle sting also contains formic acid. To neutralize, apply a base like baking soda. Acetic acid is in vinegar, citric acid in citrus fruits, lactic acid in sour milk and muscles. Formic acid is the simplest carboxylic acid.

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