Force experienced by a charge in an electric field is given by,
[tex]F_{electric}=qE[/tex]where q is the charge, E is the electric field,
Given,
[tex]\begin{gathered} q=5.0\times10^{-4}C \\ F_{electric}=2.5\times10^{-4}N \end{gathered}[/tex]Hence,
[tex]\begin{gathered} 2.5\times10^{-4}=5.0\times10^{-4}\times E \\ E=0.5\text{ N/C} \end{gathered}[/tex]