Practice MCQ Questions and answers on Chemistry-GK

The white phosphorus allotrope is the most reactive, least stable and most toxic of the three. It consists of four phosphorus molecules that chemically bond to form a tetrahedral shape.

Limestone is used as a raw-material for the manufacture of quicklime (calcium oxide), slaked lime (calcium hydroxide), cement and mortar. Clay and shale are also used as raw materials for the production of cement.

Nitrogen, required in large quantities for healthy plant growth, is supplied either as a cation (ammonium - NH₄⁺) or an anion (nitrate - NO₃^-). The ratio of these two forms of nitrogen in the nutrient solution can have large effects on both the rate and direction of pH changes with time.

In cement almost entire amount of lime is present in combined state as calcium silicates and calcium aluminates. Cement containing excess amount of lime cracks during setting while cement containing less amount of lime is weak in strength. Setting of cement is an exothermic process.

Sodium bicarbonate commonly known as baking soda, is a chemical compound with the formula NaHCO₃.

Sodium Vapour Lamps glow with yellow colour due to the emission of excess energy absorbed by sodium atoms, in the yellow region of the spectrum.

A gemstone or gem (also called a precious or semiprecious stone, a fine gem, or jewel) is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments. However certain rocks (such as lapis lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have aesthetic value. Topaz, Opal and Pearl are gemstones but Cat’s-eye is not a gem stone.

Sulphur (as sulphate) is a major plant nutrient, and is essential for crop growth. Calcium Sulphate (gypsum) is used to improve soil quality. Calcium sulphate acts as a pH buffer, which can contribute to neutralizing both soil alkalinity and acidity. It is mainly used for the reclamation of sodic soils through ion exchange (calcium replacing sodium).

Nitrate (NO₃) is the most common form of inorganic nitrogen in unpolluted waters. Nitrate moves readily through soils and into ground water, where concentrations can be much higher than in surface waters. Water in coastal areas mainly contains elementary nitrogen gas (N₂).

In silvery paints, the main constituent is aluminium powder.