QUES: Although an alloy is technically an impure metal, when referring to alloys, the term "impurities" usually denotes those elements which are not desired. These impurities are often found in the base metals or the solutes, but they may also be introduced during the alloying process. For instance, sulfur is a common impurity in steel. Sulfur combines readily with iron to form iron sulfide, which is very brittle, creating weak spots in the steel. Lithium, sodium and calcium are common impurities in aluminium alloys, which can have adverse effects on the structural integrity of castings. Conversely, otherwise pure-metals that simply contain unwanted impurities are often called "impure metals" and are not usually referred to as alloys. Oxygen, present in the air, readily combines with most metals to form metal oxides; especially at higher temperatures encountered during alloying. Great care is often taken during the alloying process to remove excess impurities, using fluxes, chemical additives, or other methods of extractive metallurgy.

What makes pure metals impure metals?
What is the answer?
ANS: unwanted impurities
QUES: Britain's first use of brass occurred around the 3rd2nd century BC. In North America, copper mining began with marginal workings by Native Americans. Native copper is known to have been extracted from sites on Isle Royale with primitive stone tools between 800 and 1600. Copper metallurgy was flourishing in South America, particularly in Peru around 1000 AD; it proceeded at a much slower rate on other continents. Copper burial ornamentals from the 15th century have been uncovered, but the metal's commercial production did not start until the early 20th century.

When did commercial production of copper begin?
What is the answer?
ANS: early 20th century
QUES: The Arena Football League (AFL) is the highest level of professional indoor American football in the United States. It was founded in 1987 by Jim Foster, making it the third longest-running professional football league in North America, after the Canadian Football League and the National Football League. It is played indoors on a 68-yard field (about half the distance of an NFL field), resulting in a faster-paced and higher-scoring game. The sport was invented in the early 1980s and patented by Foster, a former executive of the United States Football League and the National Football League.

Where does the Arena Football League rank amongst professional football leagues in North America by longevity?
What is the answer?
ANS:
third