General Science and Basic Health Knowledge
What this domain tests
General science for the MPHW-lab entrance exam covers measurement, concentration, solutions, acid-base balance, heat, electricity, and health-related science such as ORS, nutrition, and disinfection. Questions usually ask you to calculate a safe value or choose a safe practice, not just recall a definition.
Core rules
- SI units: length in metre (m), mass in kilogram (kg), volume in litre (L), amount in mole (mol). 1 L = 1000 mL and 1 mL = 1 cm³.
- Percentage concentration: % w/v means grams per 100 mL; % v/v means mL per 100 mL; % w/w means grams per 100 g.
- pH below 7 is acidic, 7 is neutral, and above 7 is alkaline. Each pH unit represents a tenfold change in hydrogen ion activity.
- Osmosis moves water across a semipermeable membrane from lower solute concentration to higher. Cells shrink in hypertonic fluid and swell in hypotonic fluid.
- Disinfection reduces pathogens on objects; sterilization destroys all microorganisms including spores. Boiling does not reliably sterilize.
- Standard ORS is preferred for dehydration. A homemade sugar-salt solution is not a substitute in severe dehydration.
Worked example
Prepare 500 mL of 0.9% w/v sodium chloride. A 0.9% w/v solution contains 0.9 g NaCl in 100 mL. For 500 mL: 0.9 g × (500/100) = 4.5 g. Weigh 4.5 g NaCl, dissolve it in about 400 mL distilled water, then make up to 500 mL. The reasoning is that percentage is a ratio to final volume, so you scale by 500/100, not by the water added.
Traps
Do not confuse w/v with v/v. Do not round 0.9% to 1% in a clinical calculation. Do not call boiling sterilization. Do not advise extra salt or sugar in ORS. Check units before calculating.