Explanation

(c)
The order of reactivity depends upon the stability of the carbocation formed $ie,\ FCH_{2}\begin{matrix}
+ \\
C
\end{matrix}HCH_{3},\ FCH_{2}CH_{2}\begin{matrix}
+ \\
C
\end{matrix}HCH_{3},\ CH_{3}\begin{matrix}
+ \\
C
\end{matrix}HCH_{3}$ and$\ Ph\begin{matrix}
+ \\
C
\end{matrix}H_{2}$. The stability order of carbocations is $Ph\begin{matrix}
+ \\
C
\end{matrix}H_{2} > CH_{3}\begin{matrix}
+ \\
C
\end{matrix}HCH_{3} > FCH_{2}{CH}_{2}\begin{matrix}
+ \\
C
\end{matrix}HCH_{3} > FCH_{2}\begin{matrix}
+ \\
C
\end{matrix}HCH_{3}$. Thus, the order of reactivity follows the order IV > III > II> I