$\begin{array}{c}{\mathrm{F}}_2\\ {\mathrm{Cl}}_2\end{array}\} \mathrm{gases}$

${\mathrm{Br}}_2\} \mathrm{liquid}$

${\mathrm{I}}_2\} \mathrm{solid}$

As we go down the group Vander Waal forces increases. 

Hence, physical state changes.