Question

The correct order of the atomic radii of C, Cs, Al and S is:
(a) $S$ < $C$ < $Al$ < $Cs$
(b) $S$ < $C$ < $Cs$ < $Al$
(c) $C$ < $S$ < $Cs$ < $Al$
(d)$C$ < $S$ < $Al$ < $Cs$

Answer 1

As we move from left to right, atomic radii decreases and as we move from top to bottom, the atomic radii increases, so identify the positions of these elements in the periodic table and then, you can easily find the increasing order of atomic radii in these elements.

Complete answer:
First of all, let's discuss what an atomic radius is. By the term atomic radius, we mean the average distance of the outermost shell from the nucleus.
The atomic decreases as we move from right to left of the periodic table and increases as we move from top to bottom of the periodic table.
The increasing order of the atomic radii of the elements C, Cs, Al and S can be easily determined with the help of the periodic table as:

1 H		2 He
3Li	4Be
11Na	12Mg
19K	20Ca	21Sc
37Rb	38Sr	39Y
55Cs	56Ba	57La

From the periodic table , we can see that the Cs( cesium) has the largest atomic radii among all, followed by aluminum; Al then carbon; C and Sulphur; S has the smallest atomic radii of all. So, the increasing order of atomic radii is;
$S$ < $C$ < $Al$ < $Cs$

Hence, option(a) is correct.

Note:
Atomic radii s divided into three types;
1. Covalent radius : the distance between the two atoms when they are bound by a single bond in a covalent molecule is called the covalent radius.
2. Van Der Waals radius: the one half the distance between the nuclei of the two non covalently bonded atoms is called the Van Der Waals radius.
3. Metallic radius: it is one half the internuclear distance between the two adjacent metal atoms.