Question

What is the valency of magnesium with atomic number $12$?
A.$2$
B.$4$
C.$5$
D.$6$

Answer 1

Hint:This question gives the knowledge about periodic table and valence shell electrons. Periodic table is basically the tabular representation of elements, which are organized by electronic configuration, atomic number and repeated chemical properties. The elements which are present in the same group experience the same electronic configuration in the valence shell.

Complete answer:
Periodic table is basically the tabular representation of elements, which are organized by electronic configuration, atomic number and repeated chemical properties. Periodic table consists of seven rows and eighteen groups. In rows, the elements are organized from left to right and in groups, elements are organized from top to bottom. In total there are $118$ elements present in the periodic table.
The number of protons present in the nucleus determines the atomic number.
Properties of periodic table are as follows:
$1$. The elements which are present in the same group experience the same electronic configuration in the valence shell.
$2$. The elements which are present in the same group experience similar chemical properties.
$3$. The elements which are present in the same period experiences increase in valence electrons.
$4$. The elements which are present in the same period experiences increase in the number of energy subshells.
$5$. In the periodic table, ionization energy decreases the group.
$6$. In the periodic table, electronegativity decreases the group.
$7$. In the periodic table, atomic radii increases the group.
Magnesium belongs to the group $2$ of the periodic table. The elements present in the group $2$ generally possesses valency as $2$. Magnesium consists of $2$ electrons in its valence shell.

Therefore, option $A$ is the correct option.

Note:
Always remember the concept that the periodic table is the representation of elements, organized by electronic configuration, atomic number and repeated chemical properties. The elements which are present in the same group experience the same electronic configuration in the valence shell.