Sketch a picture of the situation, showing the iron ion and electron.
Iron ion and electron and their position vectors.
The plan is to first calculate the the electric field due to the iron ion at the location of the electron using
Then, calculate the force on the electron due to the electric field.
The position of the electron relative to the iron ion is
The magnitude of is
The unit vector is
The electric field due to the iron atom at this location is
The force on the electron due to the electric field at this location is