Answer
\begin{matrix}
\space & ion & nºprotons & nº electrons\\
a. & O^{2-} & 8 & 10 \\
b. & K^+ & 19 & 18 \\
c. & I^- & 53 & 54 \\
d. & Na^+ & 11 & 10
\end{matrix}
Work Step by Step
1. The number of protons is determined by the symbol, using a periodic table.
a. O: 8
b. K: 19
c. I: 53
d. Na: 11
2. The charge is determined by this equation:
charge = $nº protons - nº electrons$
So:
$nº electrons = nºprotons - charge$
a. 8 - (-2) = 8 + 2 = 10 electrons
b. 19 - (+1) = 19 - 1 = 18 electrons
c. 53 - (-1) = 53 + 1 = 54 electrons
d. 11 - (+1) = 11 - 1 = 10 electrons