$\mathrm{F}>\mathrm{P}>\mathrm{Si}>\mathrm{Be}$
On moving left to right in a period valence electron increases by one. The atomic numbers are $\mathrm{F}\left(9\right),\mathrm{P}\left(15\right),\mathrm{Si}\left(14\right),\mathrm{Be}\left(4\right)$ .
By the electronic configuration
$\mathrm{F}-2,7,\mathrm{P}-2,8,5,\mathrm{Si}-2,8,4,$ $\mathrm{Be}-2,2.$
Hence $\mathrm{F}$ has 7 electrons, $\mathrm{P}$ has 5 , $\mathrm{Si}$ has 4 and $\mathrm{Be}$ has 2 electrons in their outermost shell.