A magnesium ion has a net positive charge while the magnesium atom has no charge.

The correct option is A True
Ion is defined as an atom or molecule having positive or negative charge by the loss or gain of electrons.

(i) Negatively charged ions are called anions. Example: $F^{-},O{H}^{-}$

(ii) Positively charged ions are called cations. Example: $P{b}^{+4},P{b}^{+2},F{e}^{+2},M{g}^{+2}$

Electronic configuration of $Mg$ is $2,8,2$. It loses $2$ electrons to attain octet and become stable. Hence, gets a net positive charge of $2$.

Magnesium atom with no loss of electron has no charge.