Force of attraction between K+ and O2- ions

[alexparker]

Calculate the force of attraction between a K+ and O2- ion whose centers are separated by a distance of 1.5nm

I think you use this equation Ea= -(A/r)
but I am not sure what A is

 

[Kuryakin]

You need to use columb's law. Make sure you recognise the charges for each ion aren't equal.