Question

In the case of alkali metals, the ionic character decreases in the order:

• A. $MI>MBr>MCl>MF$
• B. $MCl>MI>MBr>MF$
• C. $MF>MCl>MBr>MI$
• D. $MF>MCl>MI>MBr$

Answer 1

The correct option is C $MF>MCl>MBr>MI$

According to Fajans' rule smaller the size of the cation and greater is the size of the anion more is the covalent character of the compound. Here we are considering the same metal in each case, thus cation is same for us and we know the larger the anion, greater is its polarizability. Hence the covalent character decreases in the order $MI>MBr>MCl>MF$.
As size of the halogens increases down the group.
So the decreasing order of ionic cgaracter will be:
$MF>MCl>MBr>MI$