Question

The pair that has similar atomic radii is:
(a) Sc and Ni
(b) Ti and Hf
(c) Mo and W
(d) Mn and Re

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 step by step 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.
We can easily find the pair which has the same atomic radii 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
87Fr	88Ra	89Ac

57 La	58 Ce	59 Pr	60 Nd	61 Pm	62 Sm	63 Eu	64 Gd	65 Tb	66 Dy	67 Ho	68 Er	69 Tm	70 Yb	71 Lu
89 Ac	90 Th	91 Pa	92 U	93 Np	94 Pu	95 Am	96 Cm	97 Bk	98 Cf	99 Es	100 Fm	101 Md	102 No	103 Lr

From the periodic table , we can see that the Sc has a larger radius than the Ni, Ti has smaller radii than Hf , Mo and W have almost similar radii as they lie next to each other while we move down the group and Re has larger radii than Mn.
So, Mo and W have almost similar radii.
So, the correct answer is “Option C”.

Note: Atomic radii is 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.