Practice MCQ Questions and answers on Chemistry-GK

Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most nonspecialty grout. It usually originates from limestone. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor constituents. Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, the remainder consisting of aluminium- and iron-containing clinker phases and other compounds.

Baking Soda is Sodium bicarbonate or sodium hydrogen carbonate. It is primarily used in cooking (baking), as a leavening agent. It reacts with acidic components in batters, releasing carbon dioxide, which causes expansion of the batter and forms the characteristic texture and grain in pancakes, cakes, quick breads, soda bread, and other baked and fried foods.

The excretory system functions in ridding the body of nitrogenous (nitrogen-containing, discussed below) and other wastes. Nitrogenous wastes of animals are excreted in form of ammonia, urea, or uric acid. They are excreted in the urine. Because ammonia is so water-soluble, aquatic animals often can get rid of it just by diffusion into the surrounding water. That’s one reason why the water in your aquarium gets “bad” and needs to be changed, and why not changing the water could kill the fish. However, ammonia doesn’t readily go from body fluids into air, so terrestrial animals need other ways of getting rid of nitrogenous wastes.

Quartz is made up of a continuous framework of SiO₄ silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO₂. Tridymite and cristobalite are hightemperature polymorphs of SiO₂ that occur in highsilica volcanic rocks. Coesite is a denser polymorph of quartz found in some meteorite impact sites and in metamorphic rocks.

Urea is a nitrogenous fertilizer.

In case of OF₂, oxygen is not the most electronegative element. The fluorine is more electronegative and has an oxidation state of -1. In this case, the oxygen has an oxidation state of +2.

The oxidation number of nickel in K₄[Ni(CN)₄] is zero.

The atomic number of uranium is 92, and the mass number of the isotope is given as 238. Therefore, it has 92 protons, 92 electrons, and 238 — 92 = 146 neutrons.

The mass number is a count of the number of particles in an atom's nucleus which is made up of protons and neutrons. In other words,
Mass Number = Number of Protons + Number of Neutrons.
The atomic number is the number of protons in an atom of an element, i.e., 226 = 88 + number of Neutrons. So, the number of neutrons= 226 – 88= 138.

Sommerfeld modified Bohr's theory. According to him electrons move in elliptical orbits in addition to circular orbits.