The thermal stability of interhalogen compounds depends upon the electronegativity of the combining atoms.
\(\begin{array}{|l|c|c|c|c|}
\hline \text { Elements } & \mathrm{F} & \mathrm{Cl} & \mathrm{Br} & \mathrm{I} \\
\hline \text { Electronegativity } & 4.0 & 3.2 & 3.0 & 2.7 \\
\hline
\end{array}\)
More the difference between the electronegativity the combining atoms, more is the thermal stability. Hence the order of thermal stability is \(\mathrm{ClF}>\mathrm{ICl}>\mathrm{IBr}>\mathrm{BrCl}\).