← Home

General Science (Physics, Chemistry, Biology): key facts and practice questions

Revise General Science (Physics, Chemistry, Biology) for SSC, Railway, police and state PSC exams: the facts and distinctions that keep coming up, a one-glance revision list, and 10 practice questions with answers and explanations.

Drafted with AI assistance and fact-checked on 2026-10-15; not yet read line by line by a human editor. Spotted a mistake? Tell us. Editorial standards & corrections

Jump to practice questions ↓

Key concepts and facts

Physics - measurement and mechanics: Learn SI units as pairs: force-newton, pressure-pascal, energy-joule, power-watt, frequency-hertz, charge-coulomb, current-ampere, resistance-ohm. Instruments: barometer (atmospheric pressure), hygrometer (humidity), hydrometer (density of liquids), anemometer (wind speed), ammeter (current), voltmeter (potential difference), sphygmomanometer (blood pressure). Newton's first law is the law of inertia, the second gives F = ma, the third explains rockets. Mass is constant everywhere; weight = mg is one-sixth on the Moon. Escape velocity from Earth is 11.2 km/s. One kWh = 3.6 x 10^6 J. Pascal's law runs hydraulic brakes; capillary action lifts kerosene in a wick.
Physics - heat, sound and light: Water is densest at 4 degrees C, so ice floats. Celsius and Fahrenheit read the same at -40; body temperature is 37 degrees C = 98.6 degrees F. A thermos flask blocks conduction and convection with vacuum and radiation with silvered walls. Sound needs a medium: fastest in solids (steel about 5000 m/s), then water (1500), then air (340), none in vacuum. Audible range is 20 Hz to 20 kHz; above that is ultrasonic. An echo needs about 17 m. Doppler effect: an approaching siren sounds higher. The sky is blue and sunsets red because of scattering; a rainbow is dispersion; mirage, diamond sparkle and optical fibre are total internal reflection. Convex mirrors are rear-view mirrors; concave mirrors are used in headlights. Myopia needs a concave lens, hypermetropia convex, astigmatism cylindrical, presbyopia bifocals.
Physics - electricity and modern physics: Ohm's law V = IR. A fuse has low melting point and high resistance and sits in series with the live wire. A transformer works by mutual induction and only on AC; a motor converts electrical to mechanical energy, a generator the reverse. Alpha is stopped by paper, beta by aluminium foil, gamma needs lead. Fission (U-235) runs reactors and the atom bomb; fusion powers the Sun. Silicon and germanium are semiconductors. Roentgen discovered X-rays, Becquerel radioactivity, Marie Curie radium.
Chemistry - atom, periodic table and bonding: Electron (Thomson), proton (Rutherford; Goldstein's canal rays were an earlier clue), neutron (Chadwick), nucleus (Rutherford's gold-foil experiment). Atomic number = protons; mass number = protons + neutrons. Isotopes: same atomic number, different mass number; isobars: same mass number, different atomic number. Mendeleev used atomic mass; the modern law uses atomic number. Group 1 alkali metals, group 2 alkaline earth metals, group 17 halogens, group 18 noble gases. Ionic bond = electron transfer; covalent = sharing. Reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
Chemistry - compounds, processes and everyday chemistry: Baking soda NaHCO3; washing soda Na2CO3.10H2O; caustic soda NaOH; bleaching powder CaOCl2; plaster of Paris CaSO4.1/2H2O (from gypsum CaSO4.2H2O); quicklime CaO; slaked lime Ca(OH)2; marsh gas methane; laughing gas N2O; dry ice solid CO2; vinegar acetic acid. pH below 7 is acidic, above 7 basic; blood is about 7.4; litmus is red in acid and blue in base; phenolphthalein is pink in base. Processes: Haber (ammonia, iron catalyst), Contact (sulphuric acid, V2O5), Ostwald (nitric acid), galvanisation (zinc), vulcanisation (sulphur), hydrogenation (nickel). Alloys: brass Cu + Zn; bronze Cu + Sn; stainless steel Fe + Cr + Ni. Rusting needs both oxygen and moisture. Temporary hardness (bicarbonates) goes on boiling; permanent (chlorides, sulphates) does not. LPG is mainly butane, CNG methane; graphite conducts, diamond does not.
Biology - cell, plants and classification: Hooke named the cell, Robert Brown found the nucleus. Mitochondria are the powerhouse, ribosomes make proteins, lysosomes are suicide bags, the plant cell wall is cellulose. Mitosis gives two identical cells; meiosis halves the chromosome number. Whittaker gave the five kingdoms. In photosynthesis the oxygen comes from water. Xylem carries water, phloem carries food. Hormones: auxin (growth), gibberellin (stem elongation), cytokinin (cell division), ethylene (ripening). Stamen is male, carpel female.
Biology - human body, nutrition and disease: Ptyalin digests starch, pepsin protein, bile emulsifies fat; the liver is the largest gland. The heart has 4 chambers; RBCs live about 120 days; O negative is the universal donor, AB positive the recipient. Nephron is the unit of the kidney, alveolus of the lung. Cerebrum thinks, cerebellum balances, medulla controls heartbeat. Pituitary is the master gland; insulin from the pancreas, thyroxine from the thyroid. Adult: 206 bones, 46 chromosomes. Vitamins: A retinol (night blindness), B1 thiamine (beri-beri), B3 niacin (pellagra), B12 (pernicious anaemia), C ascorbic acid (scurvy), D calciferol (rickets), K (clotting); protein deficiency gives kwashiorkor. Bacterial: TB, cholera, typhoid; viral: polio, measles, rabies, dengue; protozoan: malaria, kala-azar; fungal: ringworm. Vectors: Anopheles (malaria), Aedes (dengue), Culex (filaria). Genetic: haemophilia, colour blindness. Jenner (smallpox vaccine), Pasteur (rabies vaccine), Fleming (penicillin), Mendel (genetics), Watson and Crick (DNA).
Traps: mass vs weight; 98.6 is Fahrenheit, not Celsius; sound does not travel in vacuum; myopia-concave, hypermetropia-convex; isotopes vs isobars; galvanisation is zinc, not tin; baking soda vs washing soda; malaria is protozoan, dengue viral; vitamin B1 vs B12; Jenner vs Pasteur; the universal donor is O negative, not O positive.

One-glance revision list

SI unit pairs to chant: force-newton, pressure-pascal, energy-joule, power-watt, frequency-hertz, charge-coulomb, resistance-ohm, magnetic flux-weber.
Mass never changes; weight = mg does. On the Moon your weight is one-sixth but your mass is the same. Escape velocity from Earth is 11.2 km/s.
Celsius and Fahrenheit meet at -40. Normal body temperature is 37 degrees C = 98.6 degrees F. Water is densest at 4 degrees C, so ice floats.
Sound: steel (about 5000 m/s) > water (1500) > air (340) > vacuum (nothing). Echo needs at least about 17 m. Above 20 kHz is ultrasonic.
Eye defects: Myopia-Concave (M-C), Hypermetropia-Convex (both start with letters later in the alphabet), astigmatism-cylindrical, presbyopia-bifocal.
Radiation penetration: alpha stopped by paper, beta by aluminium foil, gamma needs lead. Sun = fusion; reactor and atom bomb = fission.
Discoverers: electron-Thomson, proton-Rutherford (Goldstein's canal rays were an earlier clue), neutron-Chadwick, nucleus-Rutherford, X-rays-Roentgen, radioactivity-Becquerel, radium-Marie Curie.
Formula card: baking soda NaHCO3, washing soda Na2CO3.10H2O, bleaching powder CaOCl2, plaster of Paris CaSO4.1/2H2O, gypsum CaSO4.2H2O, quicklime CaO, slaked lime Ca(OH)2.
Processes and catalysts: Haber-ammonia-iron; Contact-sulphuric acid-V2O5; Ostwald-nitric acid-platinum; hydrogenation-nickel; vulcanisation-sulphur; galvanisation-zinc.
Alloys: brass = Cu + Zn, bronze = Cu + Sn, stainless steel = Fe + Cr + Ni, German silver = Cu + Zn + Ni, solder = Pb + Sn.
Vitamin-disease chain: A (retinol) night blindness; B1 (thiamine) beri-beri; B3 (niacin) pellagra; B12 pernicious anaemia; C (ascorbic acid) scurvy; D (calciferol) rickets; K clotting.
Disease-agent-vector: malaria-Plasmodium (protozoan)-female Anopheles; dengue-virus-Aedes; filaria-worm-Culex; kala-azar-protozoan-sandfly; TB-bacterium (Koch), vaccine BCG.

Lessons in depth

12 longer lessons on General Science (Physics, Chemistry, Biology), one per sub-topic, each with its key facts and a quick revision.

Practice questions

Try each question before opening the answer.

1. The SI unit of pressure is (A) Newton (B) Pascal (C) Joule (D) Watt

Answer: (B) Pascal. Pressure is force per unit area, so its SI unit is newton per square metre, named the pascal (Pa). Newton is the unit of force, joule of energy and watt of power.

2. Galvanisation is the process of coating iron or steel with a thin layer of (A) Tin (B) Zinc (C) Chromium (D) Nickel

Answer: (B) Zinc. Zinc is more reactive than iron and keeps protecting it even when the coating is scratched, so galvanised sheets resist rusting. Tin-plating is used for food cans.

3. Which cell organelle stores, modifies and packages materials made in the cell and is also involved in the formation of lysosomes? (A) Endoplasmic reticulum (B) Nucleolus (C) Golgi apparatus (D) Mitochondria

Answer: (C) Golgi apparatus. The Golgi apparatus, a system of membrane-bound sacs, stores, modifies and packages products such as proteins from the ER into vesicles and dispatches them; it also forms lysosomes. The ER mainly makes and transports these materials.

4. Which blood vessels carry blood away from the heart to the various organs of the body? (A) Veins (B) Capillaries (C) Lymph vessels (D) Arteries

Answer: (D) Arteries. Arteries carry blood away from the heart under high pressure, so they have thick, elastic walls. Veins bring blood back to the heart, and capillaries link arteries with veins.

5. The bread mould Rhizopus reproduces asexually by (A) Budding (B) Binary fission (C) Fragmentation (D) Spore formation

Answer: (D) Spore formation. Rhizopus forms round sporangia at the tips of thin threads (hyphae); these release tiny spores which grow into new Rhizopus when they land on a moist surface. The thick walls of the spores protect them until conditions are suitable.

6. Pasteurisation, which protects milk from spoiling, involves (A) adding salt and sugar to the milk (B) heating the milk for a short time and then cooling it quickly (C) boiling the milk continuously for several hours (D) adding Lactobacillus to the milk

Answer: (B) heating the milk for a short time and then cooling it quickly. In pasteurisation milk is heated for a short time and then suddenly chilled; this kills most harmful microbes and keeps the milk fresh for longer. The method is named after Louis Pasteur.

7. The number of particles (atoms, molecules or ions) present in one mole of a substance is (A) 6.022 x 10^22 (B) 3.011 x 10^23 (C) 6.022 x 10^23 (D) 6.022 x 10^24

Answer: (C) 6.022 x 10^23. One mole of any substance contains 6.022 x 10^23 particles; this fixed number is the Avogadro constant (Avogadro number).

8. A yellow turmeric (curry) stain on a white cloth turns reddish-brown when soap is scrubbed on it, and becomes yellow again when the cloth is rinsed with plenty of water. This shows that soap solution is (A) Weakly acidic (B) Strongly acidic (C) Neutral (D) Basic

Answer: (D) Basic. Turmeric is a natural indicator that turns reddish-brown in a basic medium. Soap solution is basic, so the stain turns reddish-brown; rinsing washes the soap away and the yellow colour returns.

9. How many covalent bonds are present in one molecule of ethane (C₂H₆)? (A) 6 (B) 7 (C) 8 (D) 9

Answer: (B) 7. Ethane has one C-C single bond and six C-H single bonds, giving 1 + 6 = 7 covalent bonds.

10. The distance-time graph of a body is a straight line parallel to the time axis. The body is (A) at rest (B) moving with uniform speed (C) moving with uniform acceleration (D) moving with decreasing speed

Answer: (A) at rest. A line parallel to the time axis means the distance does not change with time, so the body is at rest. Uniform speed gives a straight line inclined to the time axis.

All 480 practice questions on General Science, with answers →

Where this is tested

General Science (Physics, Chemistry, Biology) is tested in SSC, Railway, police and state PSC exams. Check the current official notification and syllabus of the exam you are preparing for to see how it is covered.

Keep practising

Try to recall the answer before opening it, then revisit the ones you missed.

Start this topic’s quiz →

Explore the lesson library