Question

Which one of the following has the largest atomic radius ?
A. $Cs$
B. $Mg$
C. $Ba$
D. $Cr$

Answer 1

Hint: Since the atom is considered a sphere , the size of atom is given by the radius of the sphere . It is a very important property as many other properties are related to it .We have to look at how atomic radius changes within a group as well as in period in order to find an answer.

Complete step by step answer:
The distance from the centre of the nucleus to the point upto which the density of the electron cloud ( probability of finding the electron ) is maximum is known as atomic radius .
The atomic radius varies as we go down a group or across a period .
When we move left to right in a period the atomic radius decreases .
And when we move from top to down in a group the atomic radius increases .
The elements which are given are :
$Cs$ is a group 1 element , $Cr$ is a sixth group element whereas $Mg$ and $Ba$ are group 2 elements .
Hence , $Cs$ has the largest atomic radius out of the given four elements as it belongs to group 1 and also is the second bottom-most element .

So, the correct answer is Option A .

Note:
As we know that atomic radius decreases as we move across a period from left to right but there is an exception as the size of inert gases are larger than halogens , this is because in case of inert gases the atomic radius is expressed in terms of van der Waals (van der Waals radius is greater than covalent radius )radius while for all the other elements it is expressed in terms of covalent radius .