Chemistry Basics MCQs

Correct Answer: CH₄

Methane, the main component of natural gas, has the formula CH₄ — one carbon atom bonded to four hydrogen atoms.

Correct Answer: HClO

Hypochlorous acid (HClO) is a weak acid (Ka about 3 × 10⁻⁸), while sulphuric acid, nitric acid and hydrochloric acid are strong acids.

Correct Answer: Salt

Salt lowers the freezing point of water, melting ice on roads; sand only adds grip.

Correct Answer: Oxygen and acetylene

Oxy-acetylene gas welding burns acetylene with oxygen; argon is a shielding gas used in arc welding, not in gas welding.

Correct Answer: Hydrogen

Hydrogen makes up about three-quarters of the universe's ordinary matter by mass.

Correct Answer: NaHCO₃

Baking soda is sodium bicarbonate, NaHCO₃; washing soda is Na₂CO₃.

Correct Answer: Carbon dioxide

Carbon dioxide turns lime water milky because it reacts with calcium hydroxide in lime water to form insoluble white calcium carbonate.

Correct Answer: Carbon dioxide

Carbon dioxide is used in the preparation of soda water: it is dissolved in water under pressure to make carbonated water.

Correct Answer: Sodium Chloride

The chemical name of table salt is sodium chloride, NaCl: a compound of one sodium atom and one chlorine atom.

Correct Answer: Hydrogen

Hydrogen is the lightest gas: with the smallest atomic mass of any element, it is lighter than helium, the next lightest gas.

Correct Answer: Nitrous Oxide

Nitrous oxide is known as laughing gas because inhaling it can produce euphoria and laughter; it is also used as an anaesthetic.

Correct Answer: H₂O

The chemical formula of water is H₂O: each molecule contains two hydrogen atoms and one oxygen atom.

Correct Answer: Au

The chemical symbol of gold is Au, from its Latin name aurum, meaning 'glow of sunrise'.

Correct Answer: Helium

Helium is the gas used in balloons: it is lighter than air, so it lifts, and unlike hydrogen it is non-flammable, so it is safe.

Correct Answer: Freon

Freon is the conventional exam answer for the gas used in refrigerators: it is the trade name for the chlorofluorocarbon refrigerants once standard in refrigeration.

Correct Answer: Argon

Argon is the gas used in fluorescent lamps: it fills the tube and, with a little mercury vapour, produces the ultraviolet light that the phosphor coating turns into visible light.

Correct Answer: Ammonia

Ammonia is the gas commonly used in fertilizers: it is the feedstock from which urea and ammonium fertilizers are made, supplying nitrogen to plants.

Correct Answer: Sublimation

Sublimation is the conversion of a solid directly into a gas, skipping the liquid stage — dry ice and camphor are the textbook examples.

Correct Answer: Argon

Argon is the gas filled in electric bulbs: this inert gas fills incandescent bulbs so the tungsten filament does not burn away in oxygen.

Correct Answer: Chloropicrin

Chloropicrin is known as tear gas: it is a lachrymator that irritates the eyes and was used as a chemical-warfare agent.

Correct Answer: Sodium Hydroxide

Sodium hydroxide is used in the preparation of soaps: it reacts with fats and oils in saponification to form soap and glycerol.

Correct Answer: Acetylene

Acetylene is the gas used in welding: burning it with oxygen gives an oxy-acetylene flame hot enough (about 3,100°C) to cut and weld metal.

Correct Answer: Acetic Acid

The chemical name of vinegar is acetic acid: household vinegar is a dilute (about 5%) solution of acetic acid in water.

Correct Answer: Mercury Vapor

Mercury vapor is the gas used in fluorescent tubes: an electric current through the vapour produces ultraviolet light, which the tube's phosphor coating turns into visible light.

Correct Answer: Ethylene

Ethylene is the gas used for ripening fruits: it is the plant hormone that triggers ripening, and it is applied commercially to ripen fruit after harvest.

Correct Answer: Sodium Bicarbonate

The chemical name of baking soda is sodium bicarbonate (NaHCO₃): it releases carbon dioxide when heated or mixed with an acid, which is why it raises baked goods.

Correct Answer: Helium

Helium is the gas used for breathing by deep-sea divers: mixed with oxygen (heliox), it replaces nitrogen and avoids nitrogen narcosis at depth.

Correct Answer: Uranium

Uranium is the element used in nuclear reactors as fuel: its fissile isotope uranium-235 splits in a chain reaction, releasing the heat that generates power.

Correct Answer: Liquid Hydrogen

Liquid hydrogen is the gas used in cryogenic engines: stored at about −253°C, it burns with liquid oxygen to give the high thrust of upper-stage rocket engines.

Correct Answer: CaSO₄·2H₂O

The chemical formula of gypsum is CaSO₄·2H₂O: hydrated calcium sulfate, the mineral from which plaster of Paris is made by heating.

Correct Answer: Gallium

Gallium is the metal liquid at room temperature besides mercury in the conventional one-liner: it melts at about 29.8°C, just above ordinary room temperature, so a warm hand can melt it.

Correct Answer: Iron

Iron is the main component of steel: steel is iron alloyed with a small amount of carbon (usually under 2%), with chromium and nickel added only in special steels such as stainless steel.

Correct Answer: NH₃

The chemical formula of ammonia is NH₃: one nitrogen atom bonded to three hydrogen atoms, a pungent gas used in fertilizers and refrigeration.

Correct Answer: Nitrous Oxide

Nitrous oxide is the gas used in anesthesia: inhaled with oxygen, it sedates and relieves pain in dentistry and surgery.

Correct Answer: 78°C

The boiling point of alcohol is 78°C: ethanol, the alcohol in drinks and spirits, boils at about 78.4°C, well below water's 100°C, which is why distillation separates them.

Correct Answer: CO + H₂

Water gas is a mixture of carbon monoxide and hydrogen (CO + H₂): it is made by passing steam over red-hot coke and was historically used as a fuel gas.

Correct Answer: Calcium Oxide

The chemical name of quicklime is calcium oxide (CaO): it is made by heating limestone (calcium carbonate), and adding water turns it into slaked lime, calcium hydroxide.

Correct Answer: Na

The chemical symbol of sodium is Na: from its Latin name natrium, not from the English name (K is potassium, Ca calcium, Mg magnesium).

Correct Answer: Neon

Neon is the gas used in fluorescent signs: an electric discharge through neon gives the bright red-orange glow of classic neon signs, while other noble gases give other colours.

Correct Answer: Helium

Helium is the gas used in balloons because it is lighter than air: it lifts the balloon, and unlike hydrogen, the other light lifting gas, it is non-flammable, so it is the safe choice for party and weather balloons.

Correct Answer: K

The chemical symbol of potassium is K: from its Latin name kalium (Na is sodium, Ca calcium, P phosphorus).

Correct Answer: Carbon dioxide

Carbon dioxide is the gas used in the preparation of soft drinks: it is dissolved under pressure to carbonate the drink, and it escapes as fizz when the bottle is opened.

Correct Answer: Sodium Carbonate

The chemical name of washing soda is sodium carbonate: its common form is the decahydrate Na2CO3.10H2O, used as a water softener and cleaning agent (sodium bicarbonate is baking soda, calcium carbonate is chalk and limestone).

Correct Answer: NaCl

The chemical formula of common salt is NaCl: one sodium ion bonded to one chloride ion, the table salt used in cooking and food preservation.

Correct Answer: C₂H₅OH

The chemical formula of ethanol is C2H5OH: the alcohol in drinks and spirits, made by fermenting sugars (CH3OH is methanol, C6H12O6 glucose, CH4 methane).

Correct Answer: Ca(OH)₂

The chemical formula of lime water is Ca(OH)2: lime water is a solution of slaked lime, calcium hydroxide, in water (CaO is quicklime, CaCO3 limestone and chalk).

Correct Answer: Fe

The chemical symbol of iron is Fe: from its Latin name ferrum (Pb is lead, Zn zinc, Cu copper).

Correct Answer: Nitrogen

Nitrogen is the gas used to preserve food items: flushing food packs with nitrogen displaces oxygen, which slows oxidation and the growth of spoilage microbes without reacting with the food.

Correct Answer: Ag

The chemical symbol of silver is Ag: from its Latin name argentum (Au is gold, Pb lead, Hg mercury).

Correct Answer: Hydrated Iron Oxide

The chemical name of rust is hydrated iron oxide: when iron corrodes in moist air it forms reddish-brown hydrated ferric oxide, roughly Fe2O3.xH2O, which flakes off and exposes fresh metal underneath.

Correct Answer: Pb

The chemical symbol of lead is Pb: from its Latin name plumbum (Pd is palladium, and Ld/Le are not element symbols).

Correct Answer: H₂O₂

The chemical formula of hydrogen peroxide is H2O2: it has one extra oxygen atom compared with water (H2O), which makes it a strong oxidiser used as a disinfectant and bleach.

Correct Answer: Hg

The chemical symbol of mercury is Hg: from its Latin name hydrargyrum, meaning liquid silver, which fits the only metal that is liquid at room temperature.

Correct Answer: Cu

The chemical symbol of copper is Cu: from its Latin name cuprum (Co is cobalt, Cr chromium).

Correct Answer: C₆H₁₂O₆

The chemical formula of glucose is C6H12O6: the simple sugar plants make in photosynthesis and the body's main fuel, broken down in respiration to release energy.

Correct Answer: O₃

The chemical formula of ozone is O3: ozone is a molecule of three oxygen atoms, formed in the stratosphere where it absorbs harmful ultraviolet radiation (O2 is ordinary oxygen gas).

Correct Answer: Oxygen

Oxygen is needed for combustion: burning is a rapid reaction with oxygen, which is why fires go out when oxygen is cut off (nitrogen is inert in air, carbon dioxide is a product of burning, not a supporter of it).

Correct Answer: Atom

The atom is the smallest particle of an element that retains its chemical properties.