Distance between ions

I am doing a homework where I am supposed to calculate estimate od distance between two ions in cytoplasm. I have only been given the concentration of an ion. Any help how I should start looking this problem?


Only solution I have been able to create is the one where you force some number out from consentration by using ion radius and assume them all to have same distance. However, this feels too, I dunno, mechanical way to solve this problem.


