Physics and Chemistry MCQs

Solved general science MCQs on units, motion, light, sound, electricity, everyday chemicals, alloys and elements, at SSC and railway general awareness level.

1. 1

   The SI unit of force is the:

   AjouleBnewtonCpascalDwatt

   Correct answer: B. newton

   One newton accelerates a 1 kg mass at 1 m/s². Joules measure energy, pascals pressure and watts power.

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2. 2

   Sound travels fastest through:

   AairBa vacuumCwaterDsteel

   Correct answer: D. steel

   Sound is fastest in solids, slower in liquids and slowest in gases; it cannot travel through a vacuum.

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3. 3

   The splitting of white light into its seven colours by a prism is called:

   AdispersionBdiffractionCreflectionDpolarisation

   Correct answer: A. dispersion

   Each colour bends by a different amount in the glass, so white light spreads into a spectrum.

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4. 4

   The watt is the unit of:

   AenergyBpowerCcurrentDresistance

   Correct answer: B. power

   One watt is one joule of energy used per second.

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5. 5

   According to Ohm's law, the current through a conductor at constant temperature is:

   Ainversely proportional to the voltageBindependent of the voltageCdirectly proportional to the voltageDproportional to the square of the voltage

   Correct answer: C. directly proportional to the voltage

   Ohm's law is V = IR, so for a fixed resistance the current rises in step with the voltage.

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6. 6

   Myopia (short-sightedness) is corrected with a:

   Abifocal lens onlyBcylindrical lensCconvex lensDconcave lens

   Correct answer: D. concave lens

   A concave (diverging) lens moves the image back onto the retina. Hypermetropia is corrected with a convex lens.

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7. 7

   The acceleration due to gravity near the Earth's surface is about:

   A6.67 m/s²B8.9 m/s²C9.8 m/s²D11.2 m/s²

   Correct answer: C. 9.8 m/s²

   g is about 9.8 m/s². 11.2 km/s is the Earth's escape velocity, a different quantity.

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8. 8

   "For every action there is an equal and opposite reaction" is Newton's:

   Asecond lawBfirst lawCthird lawDlaw of gravitation

   Correct answer: C. third law

   The third law explains, for example, how a rocket moves forward by pushing gases backward.

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9. 9

   A device that converts alternating current (AC) into direct current (DC) is a:

   AinverterBrectifierCgeneratorDtransformer

   Correct answer: B. rectifier

   A rectifier, usually made with diodes, changes AC to DC. An inverter does the reverse.

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10. 10

    The normal pH of human blood is about:

    A6.4B7.0C7.4D8.4

    Correct answer: C. 7.4

    Blood is slightly alkaline, with a pH of about 7.35–7.45.

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12. 11

    The chemical name of baking soda is:

    Asodium carbonateBcalcium carbonateCsodium chlorideDsodium hydrogen carbonate

    Correct answer: D. sodium hydrogen carbonate

    Baking soda is sodium hydrogen carbonate (NaHCO₃). Washing soda is sodium carbonate.

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13. 12

    Plaster of Paris is chemically:

    Acalcium chlorideBcalcium oxideCcalcium carbonateDcalcium sulphate hemihydrate

    Correct answer: D. calcium sulphate hemihydrate

    Plaster of Paris is CaSO₄·½H₂O; it sets hard when mixed with water, which is why it is used for casts.

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14. 13

    "Laughing gas" is the common name of:

    Anitric oxideBammoniaCnitrogen dioxideDnitrous oxide

    Correct answer: D. nitrous oxide

    Nitrous oxide (N₂O) is used as a mild anaesthetic.

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15. 14

    The lightest element is:

    AhydrogenBheliumCoxygenDlithium

    Correct answer: A. hydrogen

    Hydrogen, atomic number 1, is the lightest and most abundant element in the universe.

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16. 15

    Cooking gas (LPG) consists mainly of:

    Abutane and propaneBcarbon monoxideChydrogen and oxygenDmethane and ethane

    Correct answer: A. butane and propane

    LPG is mostly butane and propane. A strong-smelling compound is added so leaks can be noticed.

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17. 16

    Vinegar is a dilute solution of:

    Aacetic acidBtartaric acidCcitric acidDlactic acid

    Correct answer: A. acetic acid

    Vinegar contains about 5–8% acetic acid (ethanoic acid).

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18. 17

    Brass is an alloy of:

    Airon and carbonBcopper and tinCcopper and zincDaluminium and magnesium

    Correct answer: C. copper and zinc

    Brass is copper and zinc. Bronze is copper and tin, and steel is mainly iron and carbon.

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19. 18

    The most abundant metal in the Earth's crust is:

    AaluminiumBironCsodiumDcalcium

    Correct answer: A. aluminium

    Aluminium makes up about 8% of the crust. Oxygen and silicon are the most abundant elements overall.

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20. 19

    Which metal is a liquid at room temperature?

    AGalliumBMercuryCLeadDSodium

    Correct answer: B. Mercury

    Mercury is the only metal that is liquid at normal room temperature; gallium melts just above it, at about 30 °C.

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21. 20

    The image formed by a plane mirror is:

    Avirtual and magnifiedBreal and invertedCvirtual and erect, the same size as the objectDreal and diminished

    Correct answer: C. virtual and erect, the same size as the object

    A plane mirror forms an upright, same-size virtual image that appears as far behind the mirror as the object is in front.

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