Question

According to the percentage weight arrange the following in descending order in the earth’s crust?
a. ${O_2},Ca,Mg,S$
b. ${O_2},S,Mg,Ca$
c. $S,Ca,Mg,{O_2}$
d. $Ca,{O_2},Mg,S$

Answer 1

Hint: We have to first analyse the abundance of elements in the earth’s crust. While the substance of the Earth must have had the same composition as the Sun initially, now the Sun 's actual composition is very different. Also, the composition of elements in the human body and life is also very different from the beginning. All these had reflected in the abundance of elements in the earth’s crust.

Complete step by step answer:
Let us analyse the elements present in the earth’s crust;
Overall $\,99\% \,$ of the minerals are composed of eight major elements, and most of these elements are present in their combined form with other elements. These elements are extracted mainly by the metallurgical processes.

Elements name	symbol	Percentage by weight $\,(\% )\,\,$
Oxygen	$\,O\,$	$\,47\,$
Silicon	$\,Si\,$	$\,28\,$
Aluminium	$\,Al\,$	$\,8\,$
Iron	$\,Fe\,$	$\,5\,$
Calcium	$\,Ca\,$	$\,3.5\,$
Sodium	$\,Na\,$	$\,3\,$
Potassium	$\,K\,$	$\,2.5\,$
Magnesium	$\,Mg\,$	$\,2\,$

From this table we can conclude the answer.
${O_2}$ has the maximum abundance in the earth’s crust.
After that calcium and after calcium ,magnesium comes and in the last sulphur.
So according to the decreasing order
${O_2},Ca,Mg,S$
Mining is the process used for the extraction of metal buried under the earth’s crust.
There are mainly three ways by which a metal can be extracted from their ore, they are the carbon reduction and another one is reduction of molten ore with the electrolysis and the last is the reduction of the ore with a more reactive metal.

So, Option (a) is correct.

Note: It should be noted that silicates are the most common minerals in the earth's crust despite the abundance of oxygen and silicon in the crust. Note that noble gases, since they do not form part of the solid crust, are not included in the tabulate form of abundance of elements in the earth’s crust. Some elements with very low crustal amounts are also not included: technetium (atomic number $\,43\,$ ), promethium ( $\,61\,$ ) and all elements with atomic numbers greater than $\,83\,$ are also not considered.