General Science MCQ Practice

• Reason: Fleming discovered penicillin in 1928 from the mold Penicillium notatum contaminating Staphylococcus culture, leading to the first true antibiotic.
• Key concept: Serendipity in science and antibiotics; concept of selective inhibition of bacteria by penicillin (cell wall synthesis inhibitor).
• Note: No formula needed; recognition based on historical discovery and impact on medicine.
• Exam tip: Remember Fleming = penicillin; others were notable scientists in different fields.

• Why correct: Evangelista Torricelli invented the barometer in 1643 to measure atmospheric pressure using a column of mercury. It demonstrates that air has weight and exerts pressure.
• Key concept: Atmospheric pressure; mercury barometer works on P = ρ g h (pressure = density × gravity × height).
• Why others are incorrect:
  • A) Thermometer measures temperature, not pressure.
  • C) Ritcher Scale measures earthquake magnitude, not invented by Torricelli.
  • D) Bar codes are modern scanning labels, not related to Torricelli.
• Exam tip: Remember 17th century = early barometer; Torricelli linked air pressure to a mercury column.

• Reason: Graphite has a layered structure where each carbon is sp2-hybridized, forming hexagonal sheets with delocalized π-electrons. These mobile electrons move within the planes and conduct electricity.
• Key concept: Delocalized electrons in a solid lattice enable electrical conductivity.
• Other options:
  • Diamond: strong 3D covalent bonds, no delocalized electrons → insulator.
  • Sulfur: covalent molecular solid with poor mobility of charges → poor conductor.
  • Fullerene: limited conductivity unless doped or heated; not a reliable conductor in pure form.
• Exam tip: Link conductivity to structure—planar, delocalized electrons ≈ good conductor.

• Reason: Plants take up nitrogen mainly as inorganic forms: nitrate (NO3−), ammonium (NH4+) often via conversion of nitrite (NO2−) in the soil, and sometimes urea (NH2CONH2) after hydrolysis. Urea is quickly converted to ammonium, hence included.
• Key concept: Nitrogen uptake occurs as NO3− and NH4+; nitrite is an intermediate; urea becomes NH4+ before use.
• Formula/numerical note: NO3−, NO2− are different oxidation states; NH4+ is the main assimilable form.
• Exam tip: If asked about uptake forms, think inorganic N (NO3−, NH4+) and common soil N sources like urea.
• Why others are incorrect: Proteins are organic and not directly absorbed; nitrates alone omit ammonium/urea; urea alone omits nitrate/nitrite.

• Why correct: In the light reactions of photosynthesis, water is split (photolysis) to release O2. Net equation: 6CO2 + 6H2O → C6H12O6 + 6O2. The liberated O2 comes from H2O, not CO2 or glucose.
• Key concept: Oxygen evolution occurs via water splitting during photosynthesis.
• Exam tip: Remember “O2 comes from water” to avoid mistaking CO2 as the source.
• Why others are incorrect: CO2 provides carbon, not oxygen gas; glucose is a product, not the source of O2.

• Why: In a parallel circuit, the potential difference (voltage) across each branch is the same, while currents split among branches. This is due to V = IR and the parallel paths having the same end voltages.
• Key concept: Voltage is constant across parallel branches; total current = sum of branch currents.
• Other options: - A is wrong: current varies per branch. - C is vague/incorrect: electricity is not a quantity to remain constant. - D is wrong: only voltage remains constant, not the total current.
• Exam tip: If two resistors are in parallel, V is same across both; I1 and I2 depend on R.

• Correct answer: C — Molecules have inter-molecular forces. These attractions allow gas molecules to come close enough to stick together when pressure increases, forming a liquid.

• Key concept: There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal spinal nerves, totaling 31 pairs.
• Reasoning (brief): 8+12+5+5+1 = 31 pairs; note: cervical nerves include 8 pairs though there are 7 cervical vertebrae.
• Why other options are wrong: 27, 32, or 11–27 are not the sum of the five spinal regions.
• Exam tip: Remember cervical nerves = 8 pairs; all others follow vertebral segments (except the cervical twist).

• Reason: The pale yellow color of urine is due to the pigment urochrome (a breakdown product of urobilinogen).
• Key concept: Pigments formed from heme breakdown determine urine color; urochrome is the main pigment.
• Formula/numerical: Not required here; color intensity varies with hydration and concentration of urochrome.
• Why others are incorrect: - A, B, D are not pigments responsible for urine coloration (they are misnamed or irrelevant terms).

Exam tip: If asked about urine color, consider hydration level and the pigment urochrome as the primary factor.