Chemistry MCQs

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Magnetite (Fe3O4) typically contains about 70% iron by weight. It is black in color and strongly magnetic. Hematite (Fe2O3) contains about 60–70% iron. Limonite contains 35–50% iron. Siderite (FeCO3) contains about 48% iron. Magnetite is widely mined due to its high iron concentration compared to other ores.

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The term white coal was used for Hydroelectricity, particularly in Europe, because of its capability to produce more energy than any other source except coal. The term was coined by a French Engineer Aristide Bèrges.

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Group 11 elements, which include copper, silver, and gold, have been known since ancient times. These elements are found in the Earth’s crust in a free or native state, due to their low reactivity compared to other elements. This is why these elements were used by ancient civilizations for crafting tools, jewelry, and early forms of money.

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The reaction of alkali metals with water produces Hydrogen gas. These metals are part of the first group on the period table and include lithium, sodium, and potassium. They are known for their vigorous reactions with water, which results in the liberation of hydrogen gas. Along with the gas, this reaction also forms a basic alkali metal hydroxide, which gives the solution its characteristic basic or alkaline properties.

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Alcohols are organic compounds characterized by the presence of a hydroxyl group, denoted as -OH. This group consists of one oxygen atom bonded to a hydrogen atom. Due to the presence of the hydroxyl group, alcohols exhibit unique properties, such as the ability to form hydrogen bonds, making them polar. Alcohols are distinct from carboxylic acids (COOH), carbonates (COO), and carbonyl group compounds (CO).

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Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc

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The electric heating is also used to produce light, as in an electric bulb. Here, the filament must retain as much of the heat generated as is possible, so that it gets very hot and emits light. It must not melt at such high temperature. A strong metal with high melting point such as tungsten (melting point 3380°C) is used for making bulb filaments. The filament should be thermally isolated as much as possible, using insulating support, etc. The bulbs are usually filled with chemically inactive nitrogen and argon gases to prolong the life of filament. Most of the power consumed by the filament appears as heat, but a small part of it is in the form of light radiated.

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Potassium-40 is a radioactive isotope of potassium with a long half-life of 1.251×10⁹ years. The decay of this particular isotope explains the large abundance of argon (0.93%) in the Earth’s atmosphere.

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The correct answer is Chlorine. – Gammaxene (also known as Lindane) is a pesticide derived from hexachlorocyclohexane, which involves chlorine. – D.D.T. (Dichloro-Diphenyl-Trichloroethane) is a synthetic pesticide containing chlorine. – Bleaching powder (calcium hypochlorite) is a chlorine compound used for disinfection and bleaching. Chlorine is essential in various chemical processes and compounds, particularly in agriculture and sanitation.

Notes:
Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2. However, hydrogen gas is very rare in the Earth’s atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth’s gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth’s surface, mostly in the form of chemical compounds such as hydrocarbons and water. Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus, as is methane, itself a hydrogen source of increasing importance.