General Science MCQ Practice

Correct option: A

• Why this is correct: Heavy water (D2O) has a higher boiling point than ordinary water (H2O) — about 101.4°C vs 100°C — not lower. This is due to greater molecular mass and stronger O–D bonds affecting phase change.
• Key concept: Isotopic substitution changes physical properties (density, melting/boiling points) even though chemistry is similar.
• Tip: If a statement says “lower boiling point,” check against known D2O properties; commonly, D2O boils at a higher temperature.
• Regarding other options: B is true (D2O density > H2O); C is true (freezing point higher for D2O); D is not a definitive property (depends on materials/environment).

• Correct option: B — Mitochondrion. It is called the powerhouse because it generates most of the cell’s ATP through cellular respiration.
• Key concept: ATP production; mitochondria have a double membrane and cristae, and host the electron transport chain and oxidative phosphorylation.
• Note: One glucose yields about 30–32 ATP molecules overall in cellular respiration.
• Exam tip: Link “powerhouse” with ATP energy factory in cells.
• Other options: Golgi modifies/ships, Ribosome makes proteins, Lysosome digests waste—these are not primary ATP generators.

Correct option: A

• Explanation: The plasma membrane is mainly a phospholipid bilayer with embedded proteins. Phospholipids have a hydrophilic head and hydrophobic tails, forming a bilayer that provides structure and selective permeability.
• Key concept: Amphipathic nature of phospholipids drives bilayer formation.
• Why others are incorrect: Lipoprotein, phospholipo-protein, and phospho-protein are not the primary components of the membrane's basic structure.
• Exam tip: Remember “lipid bilayer” as the core; proteins are embedded within/attached to this layer.

Correct option: D

• Chloropicrin is a classic lacrimating agent used in tear gas; it irritates the eyes and mucous membranes, causing tearing and coughing.
• Key concept: lacrimatory agents cause chemical irritation of the conjunctiva and respiratory tract.
• Why others are incorrect: Ethane, Ethanol, and Ether are not standard tear gas irritants; they do not have the same diagnostic lachrymatory effect in typical riot-control formulations.
• Exam tip: Remember major lachrymants: chloropicrin is a historical and common example in MCQs.

Explanation: The vitamin that requires cobalt is Vitamin B₁₂ (cobalamin). Its active form contains a cobalt atom at its core, essential for its function in DNA synthesis and red blood cell formation. Key concept: Metal ion cofactors—cobalt in B12 acts as the active center in enzymatic reactions. Why others are incorrect: - Vitamin D: fat-soluble, no cobalt dependence. - Vitamin B2 (riboflavin): acts as a coenzyme (FAD, FMN) without cobalt. - Vitamin A: fatty acid metabolism, no cobalt involvement. Exam tip: If a vitamin mentions a metal atom in its name, check for cobalt in B12.

Correct answer: B. Zinc

• Galvanisation coats iron with zinc to act as a sacrificial anode, protecting iron from rust.
• Key concept: galvanic protection — Zn is more reactive and corrodes preferentially, forming Zn2+ and releasing electrons to protect Fe.
• Simple idea: Zn → Zn2+ + 2e−; Fe is spared because Zn corrodes first.

Exam tip: remember the coating metal must be more reactive than iron; zinc is commonly used for this purpose.

Why others are incorrect: Copper, Tin, and Aluminium do not reliably serve as sacrificial coatings for iron in standard galvanising processes.

Correct answer: A. Gold

• Reason: Gold is the most ductile metal; it can be drawn into extremely long, thin wires without breaking.
• Key concept: Ductility is the ability to deform under tensile stress without fracturing. Gold has high plasticity and low yield point among common metals.
• Why others are incorrect: Aluminium, copper, and tin are ductile but not to the same extent as gold; they fracture earlier under similar stress.
• Exam tip: Remember “gold is the most ductile” as a classic fact often tested in materials science questions.

Correct option: C

• Fathometer measures ocean depth using sonar/echo sounding.
• Key concept: Depth = (speed of sound in water × round-trip time) / 2.
• Other options:
• Hydrometer measures liquid density or specific gravity.
• Hygrometer measures humidity of air.
• Galvanometer measures electric current.

Exam tip: Remember depth-finding tools use sound; never confuse with instruments for density or humidity.

Correct option: D

• Kelvin (K) is the SI base unit for temperature. It measures absolute temperature, starting from absolute zero.
• Key concept: absolute temperature with the relation K = C + 273.15.
• Other options:
  • A. Temperature — not an SI unit, just a quantity.
  • B. Ampere — unit of electric current.
  • C. Watt — unit of power.

Exam tip: Remember Kelvin is the SI unit, Celsius is a scaled offset from it.

Explanation

• Correct option: B — Decreases.
• Key concept: Clapeyron relation dT/dP = ΔV/ΔS. For ice, melting (liquid water) is denser than ice, so ΔV = V_liq − V_sol is negative, making dT/dP negative. Hence increasing pressure lowers the melting point.
• Formula/numerical idea: dT/dP = ΔV/ΔS; negative ΔV → negative slope.
• Why others are incorrect: A and C ignore the negative slope; D is not the primary effect—the question concerns pressure, though impurities can lower melting point overall (melting-point depression) but do not reverse the pressure trend.

Exam tip: Remember the saying “Ice melts under pressure” for the pressure effect on melting point.