Answer
\begin{matrix}
\space & ion & nºprotons & nº electrons\\
a. & P^{3-} & 15 & 18 \\
b. & F^- & 9 & 10 \\
c. & Mg^{2+} & 12 & 10 \\
d. & Ca^{2+} & 20 & 18
\end{matrix}
Work Step by Step
1. The number of protons is determined by the symbol, using a periodic table.
a. P: 15
b. F: 9
c. Mg: 12
d. Ca: 20
2. The charge is determined by this equation:
charge = $nº protons - nº electrons$
So:
$nº electrons = nºprotons - charge$
a. 15 - (-3) = 15 + 3 = 18 electrons
b. 9 - (-1) = 9 + 1 = 10 electrons
c. 12 - (+2) = 12 - 2 = 10 electrons
d. 20 - (+2) = 20 - 2 = 18 electrons