Chemistry MCQ Questions with Answer for all Competitive Exams

Explanation: ​As a gemstone used in jewellery, silicon carbide is called “synthetic moissanite” or just “moissanite”. Moissanite is similar to diamond in several important respects it is transparent and hard. Moissanite has become popular as a diamond substitute and may be misidentified as diamond since its thermal conductivity is close to that of the diamond, more than any other diamond substitute.

The properties of carbon fibres, such as high stiffness, high tensile strength, low weight, high chemical resistance, high-temperature tolerance, and low thermal expansion, make them very popular in aerospace, civil engineering, military, and motorsports. ​​

Dichlorodifluoromethane (R-12) is a colourless gas and is usually sold under the brand name Freon-12, which is a chlorofluorocarbon halo-methane (CFC), used as a refrigerant and aerosol spray propellant. ​​

In photosynthesis, solar energy is converted to chemical energy. The chemical energy is stored in the form of glucose (sugar). Carbon dioxide, water, and sunlight are used to produce glucose, oxygen, and water.

Explanation: Rusting iron is a chemical change. Chemical changes are the changes in which a new product is formed and the properties of this new product are completely different from the base substances. The product formed by the chemical change cannot be reversed in its base matter Example Rusting of Iron, curding of Milk, cooking of food, burning of the candle, etc.

Explanation: Magnetic quantum number represents the number of orbitals present in the sub-shell magnetic quantum number about the orientation of the orbital.

Explanation: The compound is always formed by absorption or evolution of energy but no energy is released or absorbed during the formation of the mixture.

Explanation: Citric acid is found in the juice of citrus fruits such as lemons, limes, galpals and oranges. Lemon juice contains 7–10% citric acid.

Explanation: The rectified spirit is a mixture with a composition of 95% ethanol and 5% water. Absolute alcohol is 100% concentrated ethanol. Power alcohol is a mixture of 75-80% petrol, 20-25% ethanol, and minute amounts of aromatic compounds.

Explanation: Brass is an alloy of copper and zinc. The proportions of zinc and copper can vary between different types of brass alloys having different mechanical and electrical properties.

Explanation: Baking soda is sodium bicarbonate with the chemical formula NaHCO3. It is primarily used in the baking industry as a leavening agent.

Explanation: The main cause of the hardness of the water is the presence of Ca or Mg ions. When hard water containing these ions is treated with soap solution it reacts to form white cruddy ppt known as scum.

Explanation: A dry cell has the electrolyte immobilized as a paste, with only enough moisture in the paste to allow current to flow. The electrolyte is ammonium chloride in the form of a paste next to the zinc anode. In some more modern types of so-called ‘high power’ batteries, ammonium chloride has been replaced by zinc chloride.

Explanation: Hexane does not give sooty flame as it is an alkane and the saturated compound whereas Benzene, Naphthalene, and Anthracene are aromatic and unsaturated so they give sooty flame.

Explanation: Coke is added to the blast furnace along with iron ore in a blast furnace. Coke being derived from fossil fuel by destructive distillation. Thus it contains a higher percentage of carbon and has a high calorific value that’s why it functions as a fuel to supply heat. Coke also acts as a reducing agent and reduces metal (iron) oxide to metal.

Chemical equations involved in the process are the following:

2C(s) + O₂ (g) →2CO (g)

FeO(s) + CO (g) → Fe(s) + CO₂ (g)

Fe₂O₃ + 3CO (g) → 2Fe(s) + 3CO₂ (g)

Explanation: Ammonia (NH₃) obtained from different sources always has the same proportion of Nitrogen and Hydrogen and it proves the validity of the law of constant proportion.

Explanation: Aqueous solution of copper sulfate is acidic in nature because copper sulfate on dissolving with water, the following chemical reaction takes place

CuSO₄ (s) + 2H₂O → Cu(OH)₂ (l) + H₂SO₄ (aq)

Now as we can see in the above chemical equation the sulphuric acid generated is strong mineral acid which results in an increase in the acidity of the solution. Thus the aqueous solution of copper sulfate is acidic in nature.

Explanation: The force between protons and neutrons in the nucleus is short-range strong interaction.

Explanation: Mass number = number of proton + number of neutron ​​

12 = 6+number of neutron ​​

12 – 6 = number of neutron

∴ Number of neutron= 6

Explanation: In any atom, the atomic number represents the number of electrons which is equal to the number of protons.

Explanation: ​Zinc is much more reactive as compared to tin and may react with natural acids and bases in food materials.

Explanation: Sodium carbonate is basic salt because it is a salt of a weak acid and a strong base.

H2CO₃ + 2NaOH → Na₂CO₃ + 2H₂O

Explanation: Ammonium chloride decomposes into ammonia and hydrogen chloride gas.

​​NH₄Cl → NH₃ + HCl

It produces fumes of ammonia and hydrochloric acid.

Explanation: Covalent bonds being directional is that atoms bonded covalently prefer specific orientations in space relative to one another. As a result, molecules in which atoms are bonded covalently have definite shapes.

Explanation: The (O–H) bond in CH₃OH is Polar Covalent due to the electronegativity difference between Oxygen and Hydrogen atoms.

Explanation: ​Freezing of water is not a chemical change as ice when melt changes back to water showing the physical change.

Explanation: A trend of decreasing electron affinity going down the groups in the periodic table would be expected. The additional electron will be entering in an orbital farther away from the nucleus, and thus would experience a lesser effective nuclear charge. It is fairly obvious that the atoms get bigger as you go down the group with the increase in atomic number. The reason is equally obvious – you are adding extra layers of electrons.

Explanation: Alkali metals and Alkaline earth metals form an ionic bond while Aluminium forms a covalent bond with Cl. So the AlCl₃ molecule has a covalent bond.

Explanation: Mercuric oxides got reduced to mercury and their oxidation number changes from +2 to 0. Whereas other reactions are showing an oxidation reactions.

Explanation: Creating firework colours is a complex endeavour, requiring considerable art and application of physical science. Strontium and barium both are alkaline earth metals and are extremely reactive. They both impart characteristic colour to a flame. Strontium salts impart a red colour to fireworks. Strontium compounds are also important for stabilizing fireworks mixtures. Barium is used to create green colours in fireworks, and it can also help stabilize other volatile elements.

Explanation: Graphite is an allotropic form of the element carbon. Graphite can act as a moderator because it can slow down the speed of the neutrons so that nuclear fission reactions can be carried art in a controlled manner in nuclear readers.

Explanation: Tetraethyl lead (C₂H₅)₄Pb is used as an antiknock compound. It is mixed with petrol to improve its quality. Therefore automobile exhausts lead, which pollutes city.

Explanation: Enriched uranium are the uranium in which the component of Ratio active isotopes U235 are artificially increased. It is used in atomic reactors.

Explanation: Graphite is used as a moderator in nuclear reactors. The nuclear reactor provides us with Nuclear energy for structural works. Heavy water is also used as a moderator in Nuclear reactors.

Explanation: Acids are those substances in which Hydrogen is found and they produce Hydrogen ions in an aqueous solution. We use many natural acids in our usual life. In lemon, Orange, and grapes citric acid is found while malic acids are found in raw apples, and in milk lactic Acid is found while in Vinegar Acetic Acid (CH₃COOH) is found.

Explanation: Generally, iodized salt contains Iodine either as Potassium Iodide or Potassium Iodate.

Explanation: Stainless steel contains sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal’s internal structure.

Explanation: Phosphor bronze is used for the manufacture of springs and suspension filaments in electrical instruments.

Explanation:

Haematite – Iron (Fe₂O₃) ​​

Galena – Lead (PbS) ​​

Bauxite – Aluminium (Al (OH) ₃) ​​

Malachite – Copper (Cu₂CO₃ (OH) ₂)

Explanation: NaOH molecule contains both ionic and covalent bonds. In the NaOH molecule, Na has a positive charge while OH has a negative charge. The ionic bond is present between Na⁺ and OH^–. The covalent bond is present between O and H atoms in OH^–.

Explanation: The most effective gas of the First World War was mustard gas a vesicant, which was introduced by Germany in July 1917. Mustard gas is not a particularly effective killing agent but the skin of its victims got blistered, their eyes became very sore and they began to vomit. Mustard gas caused internal and external bleeding and attacked the bronchial tubes.

Explanation: Charcoal or coal of wood is a black Brownish Product that is formed when wood or bone is combusted in the absence of oxygen and water. Volatile constituents from animals and vegetation are removed. Charcoal is used as an adsorbent in water treatment because charcoal adsorbs the pollutants present in water.

Explanation: ​Natural gas is 95 percent Methane (CH₄) and have four other hydrocarbons: ​​Ethane (C₂H₆) – 2.5%, Propane (C₃H₈) – 0.2%, Butane (C₄H₁₀) – 0.06%, Pentanes Plus Decane (C₅H₁₂ + C₁₀H₂₂) – 0.02%. It also contains small amounts of: Nitrogen (N₂) – 1.6%, Carbon Dioxide (CO₂) – 0.7%, Hydrogen Sulphide (H₂S) – trace, Water (H₂O) – trace

Explanation: At the lowest temperature Hydrogen turns into Liquid.

Explanation: Biogas is primarily a mixture of methane (CH₄) and inert carbon dioxide gas (CO₂). The gas is produced by the anaerobic digestion or fermentation of organic matter like manure, sewage sludge, municipal solid waste, biodegradable waste, etc. It is a clean and renewable fuel.

Explanation: Petroleum products are usually grouped into three categories: light distillates (LPG, gasoline, and naphtha), middle distillates (kerosene, diesel), heavy distillates, and residuum (heavy fuel oil, lubricating oils, wax, and asphalt). Hence, the correct option would be Gasoline, kerosene, diesel.

Explanation: Formic acid is stronger than acetic acid due to its chemical composition. Formic acid is an organic acid as well as active acid in an organic acid.

Explanation: Superphosphate of lime – Ca(H₂PO₄)₂ ​​Urea – CO(NH₂)₂ ​​Indian saltpetre – KNO₃ ​​Chile saltpetre – NaNO₃

Explanation: Correct matching will be as following:

Explanation: Bisphenol A, commonly abbreviated as BPA, is an organic compound with two phenol functional groups. Bisphenol A is used primarily to make plastics which is used in making food packaging material. It is a key monomer in the production of epoxy resins and is used to make polycarbonate plastic. Polycarbonate plastic, which is clear and nearly shatter-proof, is used to make a variety of common products including baby and water bottles, sports equipment, medical and dental devices, dental fillings and sealants, eyeglass lenses, CDs and DVDs, and household electronics.

Explanation: Red phosphorus is mostly used in the manufacture of safety matches and in making smoke bombs.

Explanation: Unstable allotropes of nitrogen consisting of more than two nitrogen atoms have been produced in the laboratory, like N₃ and N₄. Under extremely high pressures (1.1 million atm) and high temperatures (2000 K), as produced under diamond anvil conditions, nitrogen polymerizes into the single-bonded diamond crystal structure, an allotrope nicknamed “nitrogen diamond”.

Explanation: Silicon is a semiconductor that means that unlike metal its electrical conductivity increases with temperature. As a semiconductor, silicon (Si) is used to make a transistor that amplifies or switch electrical currents.