General Science MCQ Practice

• Why correct: The Montreal Protocol aims to phase out ozone‑depleting substances (like CFCs) to protect the ozone layer and reduce UV radiation reaching Earth.
• Key concept: Stratospheric ozone and ozone depletion caused by anthropogenic chemicals.
• Note on options: Biodiversity (B), biological weapons (C), and European Community (D) are unrelated to this treaty.

• Execution time is the time the CPU spends processing a job—i.e., the actual CPU time to run instructions.
• Other terms: Delay time is waiting before processing starts, Real time is wall-clock elapsed time for a task in the real world, Down time is idle or non-operational period.
• Key concept: CPU time (execution time) ≈ (number of instructions) × (cycles per instruction) / clock rate.

Exam tip: If options mention wall clock vs CPU time, choose the one referring to CPU processing time.

• Correct answer: C — Seeds of Bt cotton are cheaper than non-GM seeds is not true. Bt cotton seeds are often priced higher due to technology royalties and licensing.
• Key concept: Bt cotton expresses Bacillus thuringiensis toxin, giving built-in pest resistance, reducing chemical insecticide use.
• Why C is incorrect: GM seeds usually cost more upfront, not cheaper.
• Why A, B, D are often considered true statements:
  • A: Farmer profits can increase due to higher yields and lower pest damage.
  • B: Insecticide use often declines with Bt cotton.
  • D: Cotton exports can rise due to better quality and yield, contributing to higher export volumes.
• Exam tip: Focus on price vs. benefits; GM seeds often cost more despite reduced inputs.

• Correct answer: B. Mucor
• Reason: Biofertilizers are microbes that improve nutrient availability, especially nitrogen. Rhizobium, Azotobacter, and Anabaena fix atmospheric N2, while Mucor is a fungus not known for nitrogen fixation.
• Key concept: Biological nitrogen fixation (N2 -> NH3) by microbes improves soil fertility.
• Exam tip: Look for organisms named for nitrogen fixation or plant association (Rhizobium, Azotobacter, Anabaena) vs fungi like Mucor.

• Correct answer: C – Edusat was launched in September 2004, aimed at distance education via satellite in India.
• Key concept: Satellite-based educational TV networks enable instruction beyond classroom walls, using broadcast and e-learning tools.
• Why others are incorrect: A (Oct 1988) and B (June 2001) are earlier dates not tied to Edusat; D (Mar 2008) is later than the launch.
• Exam tip: Memorize launch year and month as a pair (month-year) for tech initiatives in India.

• Why correct: A reading magnifier uses a convex lens. Shorter focal length makes a stronger magnifier, giving higher angular magnification.
• Key concept: Magnifying power M ≈ 25 cm / f (for a simple magnifier with the object at the near point). Smaller f → larger M.
• Why others are incorrect: A 50 cm convex lens has low magnification; concave lenses (B, D) reduce size (minify) and aren’t used for reading.
• Exam tip: For reading tiny print, prefer the smallest practical focal length convex lens to maximize M.

• Reason: Natural gas is a fossil fuel formed over millions of years and is not replenished on human timescales, hence non-renewable.
• Other options are renewable: Geothermal energy uses Earth's heat; flowing water (hydro) uses river/ocean movement; biomass uses organic matter that can regrow.
• Key concept: Renewable energy sources replenish naturally and sustainably, unlike fossil fuels.
• Exam tip: Distinguish fossil fuels (coal, oil, natural gas) from renewables; if it originates from ancient biological material, it’s generally non-renewable.

• The rear view mirror in vehicles is convex, giving a wider field of view but producing a diminished image.
• For a convex mirror, magnification m = image height / object height < 1, so the image is smaller than the object.
• Correct concept: magnification is less than 1; the image is virtual, upright and smaller.

• Option B and C are wrong because the image is not larger or equal in size.
• Option D is wrong because magnification is not variable with position for a convex rear-view mirror; it remains < 1.