Question

The number of valence electrons in magnesium atom are:
A. \[12\]
B. $1$
C. $2$
D. $7$

Answer 1

Hint: The number of electrons present in the outermost shell of an atom is known as the valence electrons. In other words, the electrons which are readily available for the transition during a chemical reaction are known as valence electrons. An alternate statement for the valence electrons can also be that the number of electrons that lie in the shell of highest energy.

Complete step by step answer:
 Magnesium is an element with the chemical symbol \[Mg\] and atomic number \[12\] . It is a shiny grey solid substance which bears a close physical resemblance to the other five elements in the second column which is known as the group II elements or alkaline earth metals of the periodic table. All the group II elements have the same electronic configuration in the outer electron shell and a similar crystal structure. The electronic configuration of magnesium atom is:
$Mg = 1{s^2}2{s^2}2{p^6}3{s^2}$
One other way to write the electronic configuration is the way that was proposed by Neil Bohr. It is:
$Mg = 2,8,2$
By looking at both the electronic configurations, we find that the number of electrons in the outermost shell is found to be two. In the first case, there are two electrons in the $3s$ orbital which is the orbital with the highest energy. In the second case, the M shell is the outermost shell and has two electrons in it.

Thus, the correct option is C. $2$ .

Note:
Magnesium is an element of the alkaline earth metals series or group and it is found abundantly in the earth’s crust. It tarnishes slightly when exposed to air, although, unlike the heavier alkaline earth metals, an oxygen-free environment is unnecessary for storage because magnesium is protected by a thin layer of oxide that is fairly impermeable and difficult to remove.