Question

Which of the following has the largest radius?
A. $Sr$
B. $P$
C. $Mg$
D. $A{{l}^{3+}}$
E. $M{{g}^{2+}}$

Answer 1

Hint: The metals have a larger atomic radius than the non-metals. Metals are placed on the left side of the periodic table and the nonmetals are placed on the right side of the periodic table. The atomic size of the elements can be explained by the factor of the nuclear charge.

Complete step by step answer:
The atomic radius of the atom is explained as the distance between the nucleus of the atom and the outermost electron of the element. In the periodic table, there is a trend in the atomic radius of the elements.
When we move left to right in the period of the periodic table, the atomic radius decreases because the number of electrons increases but the number of shells remains the same due to which the nuclear charge increases and the electrons get attracted towards the nucleus. When we move down the group in the periodic table, the atomic radius increases because the number of shells increases but the electrons in the shell remain the same due to which the nuclear charge decreases and the distance of the outermost electron increases.
Now, magnesium is the element of the s-block having atomic number $12$ and belongs to period three and phosphorus is the element of the p-block having atomic number $15$ and also belongs to the third period. Since both of them belong to the same period, the magnesium will be smaller due to the smaller effective nuclear charge.
Therefore, the correct answer is Magnesium

So, the correct answer is Option C.

Note: There are many types of the radius of the element that explains the distance of the electrons. These are ionic radius, covalent radius, van der Waals radius, etc and all these properties have the same trend as the atomic radius.