Chemistry MCQs

Notes:
Radium(Ra) with atomic number 88 was discovered by Marie and Pierre Curie in 1898 as Radium Chloride. However, it was Radium was isolated in its metallic state by Marie Curie and André-Louis Debierne through the electrolysis of radium chloride in 1911.

Notes:
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Rusting of Iron is a chemical change.

Notes:
Diamond and graphite are both forms of carbon but they exhibit different properties due to variations in their bonding arrangements. Diamond does not conduct electricity as each carbon atom in diamond is covalently bonded to four other carbon atoms, leaving no free electrons to conduct electricity. On the other hand, graphite is a good conductor of electricity due to its layered structure which leaves free electrons between the layers.

Notes:
Andesite is an igneous volcanic rock with intermediate composition and is not used as an ore. Chalcopyrite is a major copper ore, sphalerite is the primary ore of zinc, and cinnabar is the main ore of mercury. Andesite mainly consists of plagioclase, pyroxene, and amphibole minerals and forms in volcanic arcs associated with subduction zones.

Notes:
The correct answer is Hydrochloric Acid. When testing for adulteration of pure ghee with vanaspati or margarine, hydrochloric acid is used because it reacts with the fats present in these substances, producing a distinct color change. This method is based on the principle that the presence of unsaturated fats in vanaspati or margarine will lead to a different reaction compared to pure ghee. Hydrochloric acid is commonly used in food testing due to its effectiveness in identifying such adulterants.

Notes:
When quicklime (calcium oxide) is added to water, it reacts exothermically to form calcium hydroxide (slaked lime). This reaction produces heat and releases water vapor, which causes bubbling. The reaction can be represented as: [ ext{CaO} + ext{H}_2 ext{O}
ightarrow ext{Ca(OH)}_2 + ext{heat} ] Trivia: Quicklime is used in various applications, including steelmaking and water treatment, and was historically used in ancient construction.

Notes:
Gun metal is an alloy primarily composed of copper, tin, and zinc. Specifically, it typically contains about 88% copper, 10% tin, and 2% zinc. This alloy is known for its strength, corrosion resistance, and ability to withstand high temperatures, making it ideal for manufacturing firearms and artillery. The term “gun metal” dates back to the 15th century when it was used for cannons and other weaponry.

Notes:
Sublimation is a transition from solid to gas, bypassing the liquid phase. Iodine sublimes, producing violet vapors; naphthalene sublimes, hence its use in mothballs; and camphor also sublimes, used in medicinal and aromatic applications. Thus, all three substances exhibit sublimation upon heating, making ‘All of them’ the correct answer.

Notes:
The correct composition of biogas released through anaerobic bio-digester system is:
Methane (CH4) – 50–75 %
Carbon dioxide (CO2) – 25–50%
Nitrogen (N2) – 0–10%
Hydrogen (H2) – 0–1%
Hydrogen sulphide (H2S) – 0–3%

Notes:
Sodium carbonate is found as dry deposits and is also known as Sajimati (efflorescent soil) in India.