General Science MCQ Practice

Answer: C

• Key concept: Humans have a mixed dentition; the deciduous (milk) teeth are 20 in total.
• Why correct: Deciduous dentition consists of 4 incisors, 2 canines, and 4 molars in each jaw pair, totaling 20 teeth.
• Quick check: Eruption start ~6 months; shed around 6–12 years; permanent teeth replace them.
• Exam tip: Remember: “Milk teeth = 20; Permanent teeth = 32.”
• Why other options are wrong: A=28, B=29, D=12 do not match the standard count for deciduous teeth.

Correct answer: C) Lactic acid

• Why correct: During strenuous exercise, insufficient oxygen forces muscles to use anaerobic respiration, producing lactic acid and causing fatigue.
• Key concept: Oxygen debt and anaerobic glycolysis: glucose → lactic acid + 2 ATP (net).
• Formula hint: Glucose → Lactic acid + Energy (ATP); buildup lowers pH and impairs enzymes.
• Why others are incorrect: CO2 rises from metabolism but isn’t the main fatigue cause; creatinine relates to kidney function; ethanol is irrelevant to muscle fatigue in this context.
• Exam tip: Link fatigue to anaerobic respiration, not oxygen uptake alone.

Answer: A Reason: Adding salt to water raises its boiling point due to boiling point elevation (colligative property). The dissolved ions lower the solvent’s vapor pressure, so a higher temperature is needed to reach atmospheric pressure. The approximate relation ΔTb = i · Kb · m shows the increase, where i is the van’t Hoff factor (≈2 for NaCl) and m is molality. Why others are wrong: - B: decrease — incorrect for a non-volatile solute. - C: remains same — incorrect. - D: none of the above — incorrect. Exam tip: Remember: adding solute raises boiling point, lowers freezing point.

Correct option: C

• The gastric glands secrete pepsin in the stomach as pepsinogen, which is activated by acidic pH (HCl) to digest proteins.
• Why others are incorrect: Insulin is a pancreatic hormone; ptyalin is an old name for salivary amylase; trypsin is a pancreatic enzyme.
• Key concept: Proteolytic enzyme activation by acid in the stomach.

Explanation

• Correct answer: A — Good conductor of heat.
• Mercury quickly and uniformly transfers heat from the patient to the mercury column, giving faster and more reliable temperature readings.
• Key concept: high thermal conductivity enables quick heat transfer; also mercury expands with heat to give a readable scale, but the main clinical usefulness cited here is heat conduction.
• Why others are wrong: B dense is not essential for measurement; C electricity conduction is irrelevant; D availability is not the defining property for clinical use.

Exam tip: Focus on properties that directly influence speed and accuracy of temperature measurement.

Explanation: Kala-azar (visceral leishmaniasis) is transmitted by the bite of a sandfly. The correct vector is Phlebotomus sandfly, which carries Leishmania parasites in its saliva and transmits them to humans during feeding. Key concept: vector-borne disease transmission by blood-feeding insects.

• Why B is correct: Phlebotomus sandfly specifically transmits Leishmania donovani causing kala-azar.
• Why others are incorrect: Culex = vector for filarial/avian or dengue-like diseases; bed-bug and mites do not transmit Leishmania.

Exam tip: Remember “sandfly-borne Leishmania = kala-azar.”

Answer: A

• Correct reason: LCD stands for Liquid Crystal Display. It uses liquid crystals whose orientation changes with an electric field to modulate light, producing images on screens.
• Key concept: Phase control of light using liquid crystals; relies on anisotropic optical properties and electric-field alignment.
• Why others are incorrect:
  • B: Low Current Display – not a standard term in display technology.
  • C: Light Circuit Display – not used.
  • D: None of the above – incorrect since A is correct.
• Exam tip: Remember acronym: LCD = Liquid Crystal Display (common in screens, calculators, monitors).

Correct answer: B

• Reason: Sound in air is a mechanical wave where the displacement of air particles is parallel to the direction of travel, i.e., longitudinal waves.
• Key concept: Particle motion along the propagation direction; in air, shear (transverse) waves cannot propagate well.
• Why others are wrong: A) Transverse, C) Electromagnetic, D) Polarized are not classification of mechanical sound in air; sound is not an EM wave and polarization is not its basic nature.
• Exam tip: Remember: gases mainly support longitudinal waves; solids can support both but longitudinal is dominant in fluids like air.

• Correct answer: D
• Concept: RADAR = Radio Detection and Ranging. It emits radio waves and measures their return after reflecting from objects to detect and locate them (position, distance, speed).
• Why D is correct: It precisely describes detecting and locating airborne objects like airplanes.
• Note on others: A is sonar-based underwater detection; B is general radio receiving; C tracking satellites is not the primary use of radar in everyday contexts.
• Exam tip: Remember RADAR = detection and ranging of objects, not just communication.

Answer: C. Gamma ray

• Why correct: Gamma rays are high-energy photons emitted from the nucleus; they have the greatest penetrating power among the listed radiations, making them the most dangerous internally and externally.