1.31 deduce the charge of an ion from the electronic configuration of the atom from which the ion is formed

An atom with less then four electrons on its outer shell will want to lose electrons because that is the quickest way for it to have a full outer shell. So we know the atom will lose electrons (this makes positive ions).

Atoms with more than four electrons will gain electrons to fill their outer shell (as it is easier than losing electrons). This will result in negative ions.

Here are some examples...

Na has the electronic configuration of  2.8.1 (it has 1 electron on it's outer shell, so it is easiest to lose 1 electron to make a full outer shell). This results in the positive ion (a cation), Na+, which has the electronic configuration of 2.8

Cl has the electronic configuration of 2.8.7 (it has 7 electrons on it's outer shell, so it is easiest to gain 1 electron to make a full outer shell). This results in the negative ion (an anion), Cl-, which has the electronic configuration of 2.8.8