$\mathrm{F} > \mathrm{P} > \mathrm{Si} > \mathrm{Be}$On moving left to right in a period valence electron increases by one. The atomic numbers are $\mathrm{F}(9), \mathrm{P}(15), \mathrm{Si}(14), \mathrm{Be}(4)$ .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.