Chemistry MCQs

Question #741

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Rutherford's gold foil experiment led to the discovery of:

A. Nucleus

B. Proton

C. Electron

D. Neutron

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Correct Answer: Option A

Explanation:
Most alpha particles passed through, but a few deflected at large angles, indicating a dense, positively charged nucleus. The proton was later identified by Rutherford. Electron discovered by Thomson; neutron by Chadwick.

This question belongs to: Science chemistry

Question #742

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Niels Bohr's model introduced the concept of:

A. Quantized energy levels

B. Wave nature of electron

C. Uncertainty principle

D. Electron cloud

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Correct Answer: Option A

Explanation:
Bohr proposed that electrons revolve in certain allowed orbits with fixed energy, and they can jump between orbits by absorbing/emitting quanta of energy. This explained hydrogen spectrum. Electron cloud is quantum mechanical model; wave nature by de Broglie; uncertainty by Heisenberg.

This question belongs to: Science chemistry

Question #743

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James Chadwick bombarded beryllium with alpha particles and discovered:

A. Proton

B. Positron

C. Electron

D. Neutron

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Correct Answer: Option D

Explanation:
Chadwick (1932) produced highly penetrating neutral radiation by bombarding Be with α-particles, identified as neutrons. Reaction: ⁹Be + ⁴He → ¹²C + ¹n.

This question belongs to: Science chemistry

Question #744

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The atomic radius of chlorine is smaller than that of sulfur because:

A. Chlorine has greater nuclear charge pulling electrons closer

B. Chlorine has fewer electrons

C. Sulfur has a complete octet

D. Chlorine has more shells

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Correct Answer: Option A

Explanation:
Across period 3, S (Z=16) to Cl (Z=17) nuclear charge increases, attracting electron cloud more strongly, reducing atomic radius. Number of shells is same (3).

This question belongs to: Science chemistry

Question #745

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The element with atomic number 12 is:

A. Sodium

B. Aluminium

C. Potassium

D. Magnesium

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Correct Answer: Option D

Explanation:
Atomic number 12 = magnesium (Mg). Electronic configuration 2,8,2. It belongs to Group 2, Period 3. Sodium is 11, aluminium 13, potassium 19.

This question belongs to: Science chemistry

Question #746

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The compound formed by transfer of electrons from a metal to a non-metal is:

A. CO₂

B. KBr

C. Cl₂

D. H₂O

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Correct Answer: Option B

Explanation:
KBr is ionic; potassium (metal) transfers one electron to bromine (non-metal) forming K⁺ and Br⁻. CO₂ and H₂O are covalent (sharing). Cl₂ is covalent (nonpolar).

This question belongs to: Science chemistry

Question #747

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Which of the following salts forms an acidic aqueous solution?

A. Potassium nitrate

B. Sodium acetate

C. Ammonium chloride

D. Sodium carbonate

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Correct Answer: Option C

Explanation:
NH₄Cl is from strong acid (HCl) and weak base (NH₄OH). It hydrolyzes: NH₄⁺ + H₂O ⇌ NH₄OH + H⁺, making solution acidic (pH

This question belongs to: Science chemistry

Question #748

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A solution turns methyl orange yellow. Its pH is:

A. Exactly 7

B. Greater than 4.4

C. Between 3 and 4.4

D. Less than 3

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Correct Answer: Option B

Explanation:
Methyl orange is red in acidic (pH4.4). So yellow indicates pH above 4.4; could be neutral or basic.

This question belongs to: Science chemistry

Question #749

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The salt used in the manufacture of plaster of Paris is:

A. CaSO₄·2H₂O

B. Na₂SO₄

C. CaCO₃

D. CaOCl₂

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Correct Answer: Option A

Explanation:
Plaster of Paris is prepared by heating gypsum (CaSO₄·2H₂O) at 373 K, removing part of water of crystallization to form CaSO₄·½H₂O. CaCO₃ is limestone.

This question belongs to: Science chemistry

Question #750

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Which metal is used in the thermal process for welding railway tracks?

A. Aluminium

B. Zinc

C. Copper

D. Iron

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Correct Answer: Option A

Explanation:
Thermite reaction: Fe₂O₃ + 2Al → 2Fe + Al₂O₃ + heat. Molten iron produced fills the gap between rails. Aluminium is the reducing agent.

This question belongs to: Science chemistry

Question #751

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Graphite is a conductor of electricity due to:

A. Absence of carbon atoms

B. Delocalized electrons within layers

C. Free protons

D. Ionic bonding

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Correct Answer: Option B

Explanation:
In graphite, each carbon is sp² hybridized and bonded to three others, leaving one p-orbital electron delocalized across the layer. These free electrons allow conduction parallel to layers.

This question belongs to: Science chemistry

Question #752

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Natural gas mainly contains:

A. Ethane

B. Butane

C. Propane

D. Methane

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Correct Answer: Option D

Explanation:
Natural gas is predominantly methane (CH₄), typically 70-95%. Ethane, propane, butane are minor components. CNG is compressed natural gas.

This question belongs to: Science chemistry

Question #753

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The fuel used in a fuel cell is:

A. Hydrogen

B. Coal

C. Kerosene

D. Diesel

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Correct Answer: Option A

Explanation:
Hydrogen fuel cells combine H₂ and O₂ to produce electricity, heat, and water. It is a clean energy source. Coal, diesel, kerosene are conventional fuels burned in engines.

This question belongs to: Science chemistry

Question #754

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During electroplating of an iron spoon with silver, the anode is:

A. Iron spoon

B. Graphite

C. Platinum

D. Silver rod

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Correct Answer: Option D

Explanation:
The silver rod dissolves (Ag → Ag⁺ + e⁻) at the anode, replenishing Ag⁺ in the electrolyte, which deposits on the iron spoon (cathode). Iron spoon remains intact.

This question belongs to: Science chemistry

Question #755

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A gas at 2 atm pressure occupies 5 L. What is its volume if pressure is increased to 5 atm at constant temperature?

A. 1 L

B. 12.5 L

C. 2 L

D. 10 L

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Correct Answer: Option C

Explanation:
Boyle's law: P₁V₁ = P₂V₂ → V₂ = P₁V₁/P₂ = (2 atm × 5 L)/5 atm = 2 L. Pressure increased, so volume decreases.

This question belongs to: Science chemistry

Question #756

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The rate of effusion of gas A is 4 times that of gas B. If molar mass of B is 64 g/mol, molar mass of A is:

A. 128 g/mol

B. 4 g/mol

C. 256 g/mol

D. 16 g/mol

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Correct Answer: Option B

Explanation:
Graham's law: r_A / r_B = √(M_B / M_A). 4 = √(64 / M_A) → square both sides: 16 = 64 / M_A → M_A = 64/16 = 4 g/mol (Helium).

This question belongs to: Science chemistry

Question #757

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A catalyst that slows down a reaction is known as:

A. Autocatalyst

B. Promoter

C. Inhibitor

D. Activator

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Correct Answer: Option C

Explanation:
Inhibitors (negative catalysts) decrease reaction rate. Promoters enhance activity of a catalyst; activators increase effectiveness; autocatalysts are reaction products that catalyze the reaction.

This question belongs to: Science chemistry

Question #758

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Which enzyme is found in saliva and begins starch digestion?

A. Amylase

B. Trypsin

C. Lipase

D. Pepsin

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Correct Answer: Option A

Explanation:
Salivary amylase (ptyalin) hydrolyzes starch into maltose in the mouth. Pepsin digests protein in stomach; lipase digests fats; trypsin is pancreatic enzyme for proteins.

This question belongs to: Science chemistry

Question #759

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The process of converting bauxite into pure alumina is called:

A. Bayer's process

B. Ostwald process

C. Contact process

D. Hall-Héroult process

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Correct Answer: Option A

Explanation:
Bayer's process uses hot NaOH to dissolve alumina from bauxite, leaving behind insoluble impurities (red mud). Alumina is then precipitated. Hall-Héroult is electrolytic reduction of alumina to aluminium.

This question belongs to: Science chemistry

Question #760

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Ammonia is used in the manufacture of:

A. Soap

B. Cement

C. Fertilizers like urea and ammonium nitrate

D. Glass

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Correct Answer: Option C

Explanation:
Ammonia reacts with CO₂ to form urea, and with HNO₃ to form ammonium nitrate, both key nitrogenous fertilizers. Glass uses Na₂CO₃; cement uses CaCO₃/clay; soap uses NaOH.

This question belongs to: Science chemistry

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