Question

The ionic radii of $R{b^ + }$ and ${I^ - }$ are 1.46 and 2.16 A˚ respectively. The most probable type of structure exhibited by it is:
A. $CsCl\;type$
B. $NaCl\;type$
C. $ZnS\;type$
D. $Ca{F_2}{\text{ }}type$

Answer 1

Hint : Initially you must be aware what the ionic radii of an ion is. Secondly consider the structure of each type of element which is mentioned in the above option. Also remember that Coordination number defines the type of compound.

Complete Step By Step Answer:
Coordination number, also called Ligancy, the number of atoms, ions, or molecules that a central atom or ion holds as its nearest neighbours during a complex or complex or in a crystal.
The influence of the relative size of the coordinated molecule and the central ion is important in hydrated cations, in which the coordinating bond is mainly the electrostatic attraction of the central cation and therefore the negative end (oxygen atom) of the water molecule.
Radius ratio: $\dfrac{{{r^ + }}}{{{r^ - }}} = \dfrac{{1.46}}{{2.16}} = 0.675$
This is nearly the limiting radius ratio of 0.414-0.732.
And we know that for these types of range the coordination number is 6.
In this category the rock salt type or $NaCl\;type$ structure is seen.
Hence the correct option is B.

Note :
The ratio of the radius of cations to the radius of the anion is effectively termed as the radius ratio of the ionic solid. The significance of radius ratio is very useful in predicting the structure of ionic solids. The structure of an ionic compound depends upon stoichiometry and the size of ions as well the coordination number of the compound.