Which of the following is the decreasing order of covalent...

According to Fajan's rules, the covalent character of an ionic compound increases with the polarizability of the anion.

The polarizability of an anion increases with an increase in its size.

For halide ions, the ionic size increases down the group in the order: $\textF^{-} < \text{Cl}^{-} < \text{Br}^{-} < \textI^{-}$.

Therefore, the polarizability of the halide ions and the covalent character of the corresponding alkali metal halides increase in the same order.

The decreasing order of covalent character is $\text{MI} > \text{MBr} > \text{MCl} > \text{MF}$.

Answer: $\text{MI} > \text{MBr} > \text{MCl} > \text{MF}$