Answer: A. Oxygen
Explanation:
Oxygen - 46.6%
Oxygen is the most abundant element in the Earth's crust. Oxygen makes up 467,100 ppm (parts per million) of the Earth's crust, or 46.6%. It exists as a major compound of the silicate minerals where it combines with other elements. It also exists as a compound in carbonates and phosphates. Oxygen has industrial, medical, and commercial purposes. It is used with acetylene to cut and weld metals. It is used in hospitals to ease respiratory disease and can also be used to manufacture explosives among other numerous uses.
Silicon - 27.7%
Silicon is the second most common element present in the crust with an abundance of 276,900 ppm. It exists as a compound in the mantle and the crust. In the crust, it exists combined with oxygen to form silicate minerals. It is found in the sand which is an abundant and easily accessible resource on Earth. Silicon is also recovered from quartzite, mica, and talc. From silicon, we get silicones used in hydraulic fluids, electric insulators, and lubricants among others. Solid silicon is majorly used as a semiconductor especially in computer hardware. It is used to make transistors in the electronic industry. Silicon is used in the aluminum industry in the making of aluminum alloys. It is used in the production of ceramics, glass, cosmetics, insecticides, some types of steel, and pharmaceutical products.
Aluminum - 8.1%
At 80,700 ppm, aluminum is the third most abundant element in Earth's crust. Aluminum does not exist as a lone element, and it is found as a compound. Abundant compounds of Aluminum include aluminum oxide, aluminum hydroxide, and potassium aluminum sulfate. Aluminum is extracted from its compounds largely through the Bayer and Hall-Heroult processes. The element ideal because of its light weight and Aluminum alloys are extensively used to make utensils foils, packaging materials. It is used in the manufacture of parts of automobiles, rockets, and machinery.
Iron - 5%
Iron exists in the earth’s crust, and its composition is 50,500 ppm. Iron extracted in the form of iron ores existing in iron oxide forms such as hematite and magnetite. Blast furnaces are used to recover iron from the iron ores. Iron has many extensive applications such as the making of steel. Iron is also used to make utensils and kitchen appliances. It is also used to make cast iron and wrought iron which is extensively utilized in many industries. Iron element will always react with water and oxygen and the surface of iron is ordinarily lustrous and silvery gray, but it has a tendency of oxidizing in the open air to produce hydrated iron oxide commonly known as rust. In its purest form iron is relatively soft and is hardened and strengthened in the smelting process by adding a small percentage of carbon. The addition of carbon of between 0.002% and 2.1% will result in steel that could be 1000 times harder compared to pure iron.
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