Question

to make 100 minus charges neutral you need

Answer 1

I am assuming youre talking about electrons. If you need to make 100 negative electrons neutral, simply add 100 positive electrons to balance them out.
-100+100=0

Answer 2

If I understand you right, you're referring to the charge on an ion. For example, if we have Na with a charge of zero, that means there are the same number of positive +1 charges (protons) as -1 charges (electrons). If we remove one of Na's electrons, for example in an ionic bond, we get \[Na ^{1+}\]

Because there is a total positive charge of +11, and a negative charge of -10, these add to give us +1.

Therefore, if (and I don't think this is possible, as no element has 100 valence electrons) you have an ion with a charge 100-, that means that there are 100 more electrons then protons, and you have to remove electrons.

(Technically, you could also add protons, but by doing that you alter the identity of the ion, changing what element it is. While that is possible, it's not a part of "normal" chemistry and can be discounted unless you are doing nuclear chemistry or nuclear physics.)