Science Questions for SSC CHSL

Physics: Units, Motion, and Everyday Forces

SSC CHSL loves asking SI units and basic laws of motion. Newton's three laws appear often in disguise: a question about why we jerk forward when a bus brakes is actually Newton's First Law (inertia). Sound, light, and electricity basics also appear. Remember that sound cannot travel in vacuum but light can.

• SI unit of Force is Newton (N), Pressure is Pascal (Pa), Energy and Work is Joule (J), Power is Watt (W)
• Newton's First Law: Objects stay at rest or in motion unless acted upon by an external force (Inertia)
• Newton's Third Law: Every action has an equal and opposite reaction (rocket launch, swimming)
• Speed of light in vacuum: 3 x 10 to the power 8 metres per second
• Sound travels fastest in solids, then liquids, then gases; cannot travel in vacuum
• Archimedes Principle: A body immersed in fluid experiences upward buoyant force equal to weight of fluid displaced

Chemistry: Elements, Gases, and Everyday Reactions

Chemistry questions focus on gases and their uses, common acids and bases, metals, and chemical changes in daily life. pH scale questions are very common. Remember: pH below 7 is acidic, above 7 is basic or alkaline, exactly 7 is neutral (pure water). Household items on the pH scale are a favourite: lemon juice is acidic, soap is basic.

• Fire extinguisher uses Carbon Dioxide (CO2) because it does not support combustion
• LPG (cooking gas) is mainly Butane and Propane; CNG is mainly Methane
• Rust is formed when iron reacts with oxygen and water: Iron + Oxygen + Water gives Iron Oxide
• Baking soda is Sodium Bicarbonate (NaHCO3); used in antacids because it is basic and neutralises stomach acid
• Vinegar is dilute Acetic Acid (CH3COOH); lemon juice contains Citric Acid
• Gold and Platinum are noble metals that do not react with air or water; that is why they are used in jewellery

Biology: Human Body, Diseases, and Vitamins

Biology is the highest-scoring science area in SSC CHSL. Focus on vitamins and deficiency diseases, parts of the human body and their functions, diseases and their causative agents (virus, bacteria, etc.), and blood groups. The mnemonic ADEK for fat-soluble vitamins is a must-remember. Questions like which blood group is universal donor or which organ produces insulin appear almost every year.

• Vitamin A: Night Blindness; Vitamin B12: Anaemia; Vitamin C: Scurvy; Vitamin D: Rickets; Vitamin K: Blood clotting problems
• Fat-soluble vitamins: A, D, E, K (remember ADEK). All others (B complex, C) are water-soluble
• Insulin is produced by Pancreas (Beta cells of Islets of Langerhans); regulates blood sugar
• Universal Blood Donor: O negative; Universal Blood Recipient: AB positive
• Malaria is caused by Plasmodium parasite, spread by female Anopheles mosquito
• Tuberculosis (TB) is caused by bacterium Mycobacterium tuberculosis; treated by antibiotics

Diseases and Their Causative Agents

A very high-frequency area in SSC CHSL. Questions typically ask: which disease is caused by which agent (virus, bacteria, protozoa, fungus) or which insect spreads which disease. Know the big four mosquito-borne diseases and common viral vs bacterial diseases.

• Viral diseases: Common cold, Influenza, Dengue, Polio, Rabies, COVID-19, Hepatitis B
• Bacterial diseases: Tuberculosis, Typhoid, Cholera, Tetanus, Leprosy (Hansen's disease)
• Protozoan diseases: Malaria (Plasmodium), Amoebiasis (Entamoeba histolytica), Kala-azar (Leishmania)
• Dengue is spread by Aedes aegypti mosquito (day-biting, black-and-white striped)
• Deficiency of Iodine causes Goitre (enlarged thyroid gland)
• Scurvy (Vitamin C deficiency) causes bleeding gums; sailors on long voyages historically suffered this

Inventions and Scientific Instruments

SSC CHSL frequently asks who invented what and which instrument measures what. These are pure memory-based questions. Link the inventor to a key word or story to remember fast.

• Thermometer measures temperature; Barometer measures atmospheric pressure; Hygrometer measures humidity
• Seismograph measures earthquake intensity; Ammeter measures electric current
• Alexander Fleming discovered Penicillin (first antibiotic) in 1928
• Edward Jenner developed the first vaccine (for Smallpox)
• Louis Pasteur proved germ theory of disease and invented pasteurisation
• Albert Einstein gave Theory of Relativity; Isaac Newton gave Laws of Motion and Gravitation

• Confusing Vitamin D deficiency (Rickets in children, Osteomalacia in adults) with Vitamin A deficiency (Night Blindness). Both affect the body badly but in completely different ways.
• Mixing up universal blood donor (O negative) with universal recipient (AB positive). Remember: O is the smallest letter so it gives to everyone; AB takes from everyone.
• Thinking sound travels faster than light. Light always wins. Sound needs a medium; light does not.
• Confusing bacteria and virus: antibiotics kill bacteria NOT viruses. TB and Typhoid are bacterial so antibiotics work; Dengue and Flu are viral so antibiotics do not help.
• Assuming pH 0 is neutral. Neutral is exactly 7. pH 0 is extremely acidic (like battery acid). This causes wrong answers on basic chemistry MCQs.

• ADEK for fat-soluble vitamins: Think A Dog Eats Kibble. A=A, D=D, E=E, K=K. Everything else (B, C) washes away in water.
• For Newton's Laws: 1st Law = Lazy (things are lazy and resist change), 2nd Law = F=ma (Force makes acceleration), 3rd Law = Tit for Tat (equal and opposite reaction).
• Mosquito diseases: Aedes = Dengue + Zika (A for Aedes, D for Dengue), Anopheles = Malaria (An for Anopheles, M for Malaria), Culex = Filariasis.
• pH trick: ACid has A in it, A comes before N in alphabet, so Acid is below Neutral (below 7). Base is above 7.

• Biology fetches the most science marks in SSC CHSL. Prioritise vitamins, diseases, organs, and blood groups above everything else in science prep.
• Expect 1 to 2 questions directly on SI units or basic physics laws. They are gift questions if you have a list memorised. Do not overthink them.
• Questions on gases and their uses (CO2 for fire, O2 for breathing, N2 in chips bags to prevent staleness) are direct fact recalls. No calculation needed.
• Inventions questions are straightforward but tricky due to similar-sounding names. Focus on Fleming (Penicillin), Jenner (Vaccine), Pasteur (Pasteurisation), and Nobel (Dynamite + Nobel Prize).
• Science GK questions in recent SSC CHSL papers (2023-24) have leaned towards everyday applications: why does ice float, how does a mirror work, what causes rainbows. Relate science to real life when studying.