Chemistry MCQs

Notes:
Oxalic acid is an organic compound with the formula C₂H₂O₄. Some call it “crab acid” due to its appearance. Its condensed formula is HOOCCOOH, reflecting its classification as the simplest dicarboxylic acid.

Notes:
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.

Notes:
Barium Sulphate is the correct answer. It is used as a radiopaque contrast agent in X-ray imaging because it absorbs X-rays, making it visible on the images. Commonly referred to as “Barium Meal” when ingested for gastrointestinal studies, it helps diagnose conditions like ulcers and tumors. Barium Sulphate is insoluble in water, ensuring it remains in the digestive tract without being absorbed.

Notes:
The auto-ignition temperature of a liquid, gas or vapor is the temperature at which the substance will ignite without any external heat source. Here is the temperature of some gases: 
Methane -580 °C 
Hydrogen -560 °C 
Propane -493 °C 
Ethylene -425 °C 
Acetylene -305 °C 
Naphtha -290 °C 
Carbon disulfide -102 °C

Notes:
Pyrolusite, Braunite, Psilomelane, and Rhodochrosite are all ores of Manganese. Pyrolusite is one of the most important ores due to its high manganese content. Braunite, although a significant ore, its manganese content is less than Pyrolusite. Psilomelane and Rhodochrosite also contribute as minor ores.

Notes:
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.

Notes:
Aluminum is considered a “Green Metal” primarily due to its high recycling rate. Approximately 75% of all aluminum ever produced is still in use today, as it can be recycled indefinitely without losing quality. This process saves energy—recycling aluminum uses about 95% less energy than producing new aluminum from bauxite ore. Additionally, recycling reduces greenhouse gas emissions and conserves natural resources, making aluminum a sustainable choice in various applications.

Notes:
Pure diamond should transmit visible light and appear as a clear colorless crystal. Colors in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations (up to atomic percents). Nitrogen gives yellowish color while the Boron gives bluish color.

Notes:
L.P.G. (Liquefied Petroleum Gas) primarily consists of propane and butane. It is used as fuel for heating, cooking, and vehicles. Propane (C3H8) and butane (C4H10) are both byproducts of natural gas processing and petroleum refining. LPG is favored for its high energy content and clean-burning properties.

Notes:
It is used for softening of water, laundering, cleaning, manufacture of glass, soap, borax, paper, paints and textile It is also extensively used as laboratory reagent.