$\begin{align}  & {{F}^{-}}=19ppm\Rightarrow darsad\,jermi\,''{{F}^{-}}''\,dar\,mahlol=19\times {{10}^{-4}} \\  & \left[ {{F}^{-}} \right]=\frac{10\,a\,d}{jerm\,moli}=\frac{10\times 19\times {{10}^{-4}}\times 1}{19}={{10}^{-3}} \\  & \left[ {{F}^{-}} \right]=M\alpha \Rightarrow {{10}^{-3}}=0/01\times \alpha \Rightarrow \alpha =0/1 \\ \end{align}$