You are confronted by a phosphorus atom. this atom has 15 protons and 17 neutrons. how many electrons does it have

15 electrons if it is not an ion

Atom:Proton number same as number of electron.

Ion:Electronic configuration becomes "2.8.8" because the atom configuration is "2.8.5" the last shell have 5 electrons is more than "3" so you need to add electrons TILL the maximium that shell can hold to make it stable.If for example if the configuration is "2.8.3" you take the 3 electrons out from the last shell in order to make it stable.

Take out:1,2,3 electrons

Add:4 electron and above depends on what shell,but of course don't add MORR when is at the max the shell can hold.