Question

What is an atom that has gained or lost electrons?

Answer 1

Hint: It refers to an atom, particle or molecule along with a net electrical charge. An Ion is defined as an atom which has gained or lost electrons, thus it possesses an overall charge.

Complete answer:
If an atom gains electrons, it's overall charge then becomes negative whereas if an atom loses electrons, then it's overall charge becomes positive.
Basically, when an atom gains or loses an electron, thus it attains a net charge and becomes an ion. When electrons get lost (or donated), the resulting ion is termed as ‘cation’ and in case when electrons are gained, the resulting ion is referred to as an anion. Therefore, cations possess a net positive charge, and anions possess a net negative charge.

Note:
When the chemical formula for an ion is written, then its net charge is written in superscript immediately after the chemical structure for the molecule/atom. The net charge is written with the magnitude before the sign; that is, a doubly charged cation is indicated like ${2^ + }$ instead of $^ + 2$. However, the charge’s magnitude is omitted for singly charged molecules or atoms; for example, the sodium cation is indicated like $N{a^ + }$ and not $Na + $.