What is a rule for making a positive ion which has positive charge?

A positve ion ( Cation) usually wants to give up an elctron.

So if it has only 1 valance it will hapilly give it up to have a nobel gas config.

Explanation:

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.