Question

Which of the following represents an ion
4He
Ca
Mg
Na+

Answer 1

The answer is Na⁺.

Na⁺ is a positive ion of sodium that is due by the loss of one electron.
4He represents four atoms of helium. It is an idel gas, that do not form elementary molecules and exist in atom form.
Ca represent one atom of calcium and Mg one atom of magnesium. They are metals and do not form elementary molecules.

Answer 2

Answer:

Na+

Explanation:

Atoms may loose or gain electrons in order to attain octate.

Chemical species obtained after loosing or gaining electrons are called ions.

When an element losses electrons, positively charged ion is formed.

When an element gains electrons, negatively charged ion is formed.

Among the given, only Na+ carry a positive charge, rest are neutral.

Therefore, Na+ is an ion.