Practice MCQ Questions and answers on Chemistry-GK

An alloy is a mixture or metallic solid solution composed of two or more elements. So they are heterogeneous systems. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal (heat treatment) history. Alloys usually have different properties from those of the component elements.

Galena, also called lead glance, is the natural mineral form of lead(II) sulphide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms.

Magnetite is the best quality of iron ore and contains 72% pure iron. Haematite contains 60% to 70% pure iron ore.

Bauxite is an alloy of aluminium.

The term hardened steel is often used for a medium or high carbon steel that has been given the heat treatments of quenching followed by tempering. The quenching results in the formation of metastable martensite, the fraction of which is reduced to the desired amount during tempering. This is the most common state for finished articles such as tools and machine parts. In contrast, the same steel composition in annealed state will be softer as required for forming and machining. Carbon steels which can successfully undergo heat-treatment have carbon content in the range of 0.30–1.70% by weight. Trace impurities of various other elements can have a significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular make the steel red-short.

Wrought iron is purest form of iron.

Cast iron has the maximum percentage of carbon.

Stainless steel is an alloy of chromium, carbon and iron.

Iron is extracted from Haematite.

Wrought iron is purest form of iron. It contain 99.5% iron, 0.25% carbon and 0.25% other impurities of S, P, Si etc.