RRB NTPC — Science MCQs Q101–Q250

Electromagnetic waves (light, radio, X-rays) travel through vacuum. Sound, water and seismic waves need a material medium.

Volt (V) is the SI unit of potential difference. 1 V = 1 J/C (energy per unit charge).

At the highest point all kinetic energy is converted to potential energy. The velocity momentarily becomes zero before the body begins to fall.

Diffraction is the bending of waves around corners and obstacles. It is most pronounced when the obstacle size is comparable to the wavelength.

An electric generator uses electromagnetic induction to convert rotational (mechanical) energy into electrical energy. A motor does the reverse.

VIBGYOR — Violet has the shortest wavelength and highest frequency; Red has the longest wavelength and lowest frequency.

Power = Work / Time. 1 Watt = 1 Joule per second. Named after James Watt.

A concave mirror produces an erect, virtual and magnified image when the object is placed between the pole and the focus. Used in shaving mirrors.

The speed of light in vacuum (c) ≈ 3 × 10⁸ m/s = 300,000 km/s. It is the universal speed limit.

Fleming's Left-Hand Rule (motor rule): thumb = force direction, index = field, middle = current. Used in electric motors.

The Law of Conservation of Energy states energy can neither be created nor destroyed, only transformed from one form to another.

A pinhole camera (camera obscura) produces a real, inverted image because light travels in straight lines through the tiny aperture.

Pascal's Law: pressure applied to enclosed fluid transmits equally in all directions. Hydraulic brakes, jacks and lifts use this principle.

When light travels from denser to rarer medium, if angle of incidence ≥ critical angle, total internal reflection occurs. Used in optical fibres.

Barometer measures atmospheric pressure. Mercury barometer was invented by Torricelli. Standard atmosphere = 101,325 Pa ≈ 760 mmHg.

A transformer uses mutual electromagnetic induction between primary and secondary coils to step up or step down AC voltage.

Decibel (dB) measures sound intensity. 0 dB = threshold of hearing; 120 dB = threshold of pain; normal conversation ≈ 60 dB.

Stars twinkle due to atmospheric refraction — the continuous variation of the atmosphere's refractive index bends starlight in different directions.

Myopia (short sight) is corrected with a diverging (concave) lens that shifts the image back onto the retina. Hypermetropia uses convex lens.

Hertz (Hz) = cycles per second. Named after Heinrich Hertz. Audible range: 20 Hz–20,000 Hz. Ultrasound: >20,000 Hz.

Newton's Third Law: every action has equal and opposite reaction. Exhaust gases pushed backward propel the rocket forward.

All warm bodies emit infrared radiation. Night-vision cameras detect IR and convert it to a visible image — no visible light needed.

Moon's gravity ≈ 1.62 m/s² which is about 1/6 of Earth's 9.8 m/s². That is why objects weigh less on the Moon.

In metallic conductors, loosely bound valence electrons (free electrons) drift in response to an electric field, constituting electric current.

Refraction at the water-air interface bends light rays, making the object appear shallower (raised) than its actual position.

The unit of electrical resistance is the Ohm (Ω), named after Georg Simon Ohm. 1 Ω = 1 V/A.

Sound is a mechanical wave requiring a material medium. In vacuum there are no particles to vibrate, so sound cannot propagate.

A concave (diverging) lens always produces a virtual, erect and smaller image regardless of object position — used in spectacles for myopia.

Loudness is related to the amplitude of the sound wave. Greater amplitude → greater loudness. Pitch depends on frequency.

Ammeter directly measures current and is connected in series. A galvanometer detects small currents and can be converted to an ammeter or voltmeter.

Dispersion occurs because different wavelengths of light refract at slightly different angles. Violet deviates most, red least. Result: VIBGYOR spectrum.

Work = Force × Displacement. 1 Joule = 1 Newton × 1 Metre. Named after James Prescott Joule.

The Sun fuses hydrogen nuclei (protons) into helium, releasing enormous energy per E=mc². Nuclear fusion requires extremely high temperature and pressure.

Bernoulli's theorem: for an ideal fluid, the sum of pressure energy, kinetic energy and potential energy per unit volume remains constant. Explains aeroplane lift.

J.J. Thomson discovered the electron in 1897 using cathode ray tube experiments. He measured the charge-to-mass ratio (e/m) of electrons.

Convex mirrors give a wider field of view and always form erect, diminished virtual images — ideal for rear-view mirrors in vehicles.

Liquid pressure P = ρgh, where ρ = density, g = gravity, h = depth. Pressure increases with depth — that is why deep-sea fish can't survive at surface pressure.

Protons (+1 charge) and neutrons (0 charge) are in the nucleus. The atomic number = number of protons, which defines the element.

Pitch is the perceived highness/lowness of a sound. High frequency → high pitch (shriller). Amplitude determines loudness.

Coulomb (C) is the SI unit of electric charge. 1 C = charge transferred in 1 second by 1 Ampere. Named after Charles-Augustin de Coulomb.

Water (H₂O): H₂ contributes 2 g, O contributes 16 g. Mass ratio H:O = 2:16 = 1:8. Volume ratio (gas) H:O = 2:1.

N₂O (nitrous oxide) is called laughing gas due to euphoric effects. It is used as an anaesthetic in dentistry.

Sodium chloride (NaCl) is common salt. It is an ionic compound formed from Na⁺ and Cl⁻ ions arranged in a crystal lattice.

SO₂ (from burning fossil fuels) and NOₓ (from vehicles/industry) dissolve in rain to form H₂SO₄ and HNO₃ — acid rain (pH < 5.6).

Aluminium (~8%) is the most abundant metal in Earth's crust. Overall: Oxygen (46%) > Silicon (28%) > Aluminium (8%) > Iron (5%).

Stainless steel contains iron + chromium (≥10.5%) + nickel. The chromium forms a protective oxide layer preventing rust.

Diamond is the hardest natural substance (10 on Mohs scale) due to its tetrahedral crystal structure. Both diamond and graphite are allotropes of carbon.

Baking soda = NaHCO₃ (sodium bicarbonate / sodium hydrogen carbonate). It releases CO₂ on heating, causing dough to rise.

Brass = Copper + Zinc. Bronze = Copper + Tin. Solder = Lead + Tin. German silver = Copper + Zinc + Nickel.

Heavy water (D₂O) contains deuterium (²H) instead of ordinary hydrogen. It is used as moderator in CANDU reactors to slow neutrons.

Zn + H₂SO₄ → ZnSO₄ + H₂↑. Hydrogen gas is liberated. This is a classic laboratory method for preparing hydrogen gas.

pH = 7 is neutral (pure water). pH < 7 = acidic. pH > 7 = basic/alkaline. pH scale ranges from 0–14.

Haber process: N₂ + 3H₂ → 2NH₃. Nitrogen (from air) reacts with hydrogen (from methane) over iron catalyst at 400–500°C to produce ammonia for fertilisers.

Au comes from Latin 'Aurum'. Ag (silver) = Argentum; Fe (iron) = Ferrum; Cu (copper) = Cuprum; Pb (lead) = Plumbum.

Bleaching powder (CaOCl₂) = Ca(OH)₂ + Cl₂. Its active component is Ca(OCl)₂ which releases Cl₂/nascent O on contact with acids/water.

CO₂ blankets the fire, cutting off oxygen supply. Its density (~1.5× air) helps it settle around the burning material. It also cools the fuel.

Washing soda = sodium carbonate decahydrate (Na₂CO₃·10H₂O). Used for softening water and in detergents. Baking soda = NaHCO₃.

Hydrogen (H) has atomic number 1 (1 proton, 1 electron). It is the lightest and most abundant element in the universe.

Galvanisation coats iron with zinc to prevent rust. Zinc acts as a sacrificial anode — it corrodes preferentially, protecting the iron beneath.

UV-B radiation from sunlight triggers synthesis of Vitamin D₃ (cholecalciferol) in the skin from 7-dehydrocholesterol. Deficiency causes rickets.

Vinegar = 4–8% acetic acid (CH₃COOH) in water. It is produced by acetic acid fermentation of dilute alcohol by Acetobacter bacteria.

Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (by yeast/zymase). Anaerobic process used in brewing, winemaking and bread-making.

The ozone layer (O₃) is in the stratosphere at 15–35 km altitude. It absorbs harmful UV-B and UV-C radiation from the Sun. CFCs deplete it.

Plaster of Paris (POP) = CaSO₄·½H₂O. Heating gypsum to 120°C removes 3/4 of its water. POP sets hard by re-absorbing water.

Graphite has layered structure; layers slide easily over each other making it an excellent dry lubricant. Also used in pencils and electrodes.

Stomach (gastric juice) contains HCl at pH 1.5–3.5. It kills bacteria, activates pepsinogen → pepsin for protein digestion.

CaCO₃ (calcium carbonate) is marble, limestone and chalk. CaO = quicklime; Ca(OH)₂ = slaked lime; CaSO₄·2H₂O = gypsum.

Neon glows reddish-orange when electricity passes through it. Other gases for coloured signs: argon (blue/purple), helium (yellow), krypton (white).

Milk of magnesia = Mg(OH)₂ suspension. It neutralises excess stomach acid (HCl). Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O.

Teflon = PTFE. The C-F bond is extremely strong and unreactive — nothing sticks to it. Also used in bearings and electrical insulation.

Rust forms when iron reacts with oxygen and water. Its exact composition is hydrated iron(III) oxide. Both O₂ and H₂O are necessary.

Helium is preferred over hydrogen for balloons because it is non-flammable and provides nearly the same lift. Hydrogen is flammable (Hindenburg disaster).

Distillation purifies water by boiling (evaporation) then cooling (condensation). Salts and impurities remain in the flask; pure water collects.

CaC₂ + 2H₂O → Ca(OH)₂ + C₂H₂↑. Acetylene (C₂H₂) is used in oxyacetylene welding and unripe fruit ripening.

Mercury (Hg) is the only metal liquid at room temperature (melting point -39°C). Bromine is the only non-metal liquid at RT.

Glucose (C₆H₁₂O₆) is a simple sugar (monosaccharide). Sucrose = C₁₂H₂₂O₁₁; Acetic acid = CH₃COOH; Ethanol = C₂H₅OH.

Neon emits characteristic orange-red light when excited electrically. It is the basis for neon signs used in advertisements.

Vitamin C = ascorbic acid. Deficiency causes scurvy. Vitamins: A=Retinol, B1=Thiamine, B12=Cobalamin, C=Ascorbic acid, D=Calciferol, E=Tocopherol.

H₂O has covalent O-H bonds (shared electrons). Water also exhibits hydrogen bonding between molecules, giving it unusually high boiling point.

Natural gas is ~80–95% methane (CH₄). CNG (compressed natural gas) and LNG (liquefied natural gas) used as vehicle fuels are mainly methane.

Green vitriol = ferrous sulphate (FeSO₄·7H₂O). Blue vitriol = CuSO₄·5H₂O. White vitriol = ZnSO₄·7H₂O. Oil of vitriol = H₂SO₄.

LPG is mainly propane (C₃H₈) and butane (C₄H₁₀). Domestic LPG cylinders in India contain predominantly butane.

Dry ice = solid CO₂ (sublimes at -78.5°C directly to gas without melting). Used as refrigerant in food preservation and for stage fog effects.

Calcium ions (Ca²⁺) are essential cofactors in the blood coagulation cascade — converting prothrombin to thrombin and fibrinogen to fibrin clot.

CO₂ is heavier than air and blankets the fire, cutting off oxygen supply. It is used in fire extinguishers, especially for electrical and oil fires.

Insulin is produced by beta cells of islets of Langerhans in the pancreas. It lowers blood glucose by promoting uptake into cells.

Mitochondria produce ATP (cellular energy currency) through aerobic respiration. They have their own DNA and double membrane.

Malaria is caused by Plasmodium (P. falciparum most dangerous) transmitted by female Anopheles mosquito. Dengue is viral, typhoid is bacterial.

Skin is the largest organ (1.5–2 m²). Among internal organs, liver is largest. Functions: protection, temperature regulation, vitamin D synthesis.

DNA carries genetic information. Its double helix structure was discovered by Watson and Crick (1953) based on X-ray data by Rosalind Franklin.

Photosynthesis: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Occurs in chloroplasts containing chlorophyll (green pigment).

Normal body temperature = 98.6°F = 37°C. Temperature regulation (thermoregulation) is controlled by the hypothalamus in the brain.

Blood group O has no A or B antigens on red blood cells — can be donated to all groups. AB is the universal recipient (has both A and B antigens).

Cerebellum (little brain) maintains balance, coordinates voluntary movements and posture. Cerebrum handles thinking; medulla controls involuntary functions.

Vitamin A (retinol) is needed for rhodopsin synthesis in rod cells of the retina. Deficiency causes night blindness and xerophthalmia.

Genetics was founded by Gregor Mendel (laws of inheritance, 1865). Modern genetics encompasses molecular biology, genomics and biotechnology.

Each kidney has ~1 million nephrons. Nephron = Bowman's capsule + glomerulus + tubules. Filters blood and produces urine.

Alexander Fleming discovered penicillin in 1928 when he noticed Penicillium mould inhibiting bacterial growth. First antibiotic in clinical use.

Haemoglobin has iron (Fe²⁺) in its haem group that binds O₂. Each RBC has ~280 million Hb molecules. Iron deficiency → anaemia.

Cell is the basic structural and functional unit of all living organisms. Robert Hooke coined the term 'cell' in 1665 observing cork under microscope.

Anaerobic respiration in yeast: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. CO₂ makes bread rise (when yeast is added to dough).

BCG (Bacillus Calmette-Guérin) vaccine protects against tuberculosis (TB) caused by Mycobacterium tuberculosis. Given at birth in India.

Dengue (viral disease) is transmitted by Aedes aegypti mosquito. Malaria = Anopheles; Filariasis = Culex; Both bite in different times of day.

Femur (thigh bone) is the longest and strongest bone. Adult femur ≈ 45 cm. Smallest bone: stapes (stirrup) in the middle ear.

Normal human somatic cells have 46 chromosomes (23 pairs). Gametes (sperm/egg) have 23. Down syndrome has 47 chromosomes (trisomy 21).

Transpiration: water loss from leaves through stomata. It creates a pull (transpiration pull) that helps draw water from roots to leaves against gravity.

HIV destroys CD4+ T-helper cells, weakening the immune system. AIDS is the advanced stage of HIV infection. Discovered in 1983 by Montagnier and Gallo.

Retina contains rods (low-light/black-white) and cones (colour vision). The fovea has the highest density of cones — point of sharpest vision.

PTH (from parathyroid glands) raises blood calcium by releasing Ca from bones and increasing absorption in intestines. Calcitonin lowers blood calcium.

Typhoid = Salmonella typhi (food/waterborne). Cholera = Vibrio cholerae; TB = Mycobacterium; Pneumonia = Streptococcus/pneumococcus.

Salivary amylase (ptyalin) converts starch → maltose in the mouth. Optimal pH ≈ 6.7–7. Pepsin digests protein in stomach; lipase digests fats.

Pituitary (hypophysis) is called master gland — it controls other endocrine glands through tropic hormones. Hypothalamus controls the pituitary.

Adrenaline (epinephrine) is the 'fight or flight' hormone secreted by adrenal medulla. It increases heart rate, blood pressure and blood glucose.

Small intestine (duodenum, jejunum, ileum) is the main site of digestion and nutrient absorption. Villi and microvilli increase surface area 600× for absorption.

Plant cell walls are primarily cellulose (polysaccharide). Fungal cell walls = chitin; Bacterial cell walls = peptidoglycan. Animal cells have no cell wall.

Carl Linnaeus (1707–1778) developed binomial nomenclature and taxonomic hierarchy: Kingdom → Phylum → Class → Order → Family → Genus → Species.

Vitamin K is needed for synthesis of clotting factors (II, VII, IX, X) in the liver. Deficiency causes excessive bleeding. Found in green leafy vegetables.

White blood cells (leucocytes) include lymphocytes (produce antibodies), neutrophils (phagocytosis) and monocytes. RBCs carry O₂; platelets aid clotting.

Human heart: 2 atria (upper) + 2 ventricles (lower) = 4 chambers. Fish heart = 2 chambers; Amphibian heart = 3; Reptile = 3 (crocodile has 4).

Ribosomes translate mRNA into proteins. They are found in all cells (prokaryotes and eukaryotes). Called 'protein factories' of the cell.

B1 (thiamine) → Beriberi; B2 (riboflavin) → Ariboflavinosis; B3 (niacin) → Pellagra; B12 → Pernicious anaemia; C → Scurvy; D → Rickets.

Golgi body (apparatus) modifies, packages and dispatches proteins received from rough ER. Called the 'post office' of the cell.

Felis catus = domestic cat; Canis lupus familiaris = dog; Panthera tigris = tiger; Homo sapiens = modern human.

Adrenaline (epinephrine) is the 'fight or flight' emergency hormone. It rapidly mobilises energy and prepares the body for sudden physical activity.

Osmosis: water moves from dilute solution (low solute) to concentrated solution (high solute) across a semipermeable membrane. Vital for plant water uptake.

Vitreous humour (jelly-like) fills the posterior chamber behind the lens. Aqueous humour fills the anterior chamber between the cornea and lens.

Pancreas: Exocrine part secretes digestive enzymes into the duodenum; Endocrine part (islets of Langerhans) secretes insulin and glucagon into blood.

Chlorophyll has Mg²⁺ at its porphyrin ring centre — analogous to haemoglobin's Fe²⁺. Mg is essential for photosynthesis and chlorophyll synthesis.

Medulla oblongata (brainstem) controls involuntary/autonomic functions: heartbeat, respiration, swallowing, blood pressure. It connects brain and spinal cord.

Oxidative phosphorylation in the inner mitochondrial membrane uses electron transport chain + O₂ to synthesise ATP. Produces ~34 ATP per glucose molecule.

Crossing over (chiasmata) during prophase I of meiosis exchanges chromosomal segments between homologous chromosomes — creating genetic diversity.

Urochrome (a pigment derived from urobilin — a breakdown product of haemoglobin) gives urine its characteristic yellow colour.

After fertilisation, the ovary wall (pericarp) develops into the fruit. Ovules inside the ovary develop into seeds. Sepals and petals usually wither.

Charles Darwin published 'On the Origin of Species' (1859) explaining evolution by natural selection — 'survival of the fittest'. Alfred Wallace proposed similar ideas.

Tendon = muscle to bone (e.g., Achilles tendon). Ligament = bone to bone. Both are made of collagen fibres. Cartilage cushions joints.

Iodine deficiency causes goitre (enlarged thyroid gland) because the thyroid cannot produce sufficient thyroxine. Iodised salt prevents goitre.

Bile is produced by hepatocytes in the liver and stored in the gall bladder. Released into the duodenum to emulsify dietary fats for digestion.

Vaccination = artificial active immunity. It introduces antigens (weakened/killed pathogen) to stimulate the body's own antibody production and memory cells.

Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Oxygen is released as a by-product of water splitting (photolysis). Respiration is the reverse reaction.

Entomophily = insect pollination (bees, butterflies). Anemophily = wind. Hydrophily = water. Ornithophily = birds. Chiropterophily = bats.