How does an atom become a positively charged ion?

Ions form when atoms gain or lose electrons. Since electrons are negatively charged, an atom that loses one or more electrons will become positively charged; an atom that gains one or more electrons becomes negatively charged. ... The metals form positively-charged ions and the non-metals form negatively-charged ions.

The answer should be c.

29.1-12=17.1the answer is this one