Chapter 2, Problem 33E

Which of the following species has
a. equal numbers of neutrons and electrons;
b. protons, neutrons, and electrons in the ratio 9:11:8;
c.a number of neutrons equal to the number of protons plus one-half the number of electrons?
$\text{M}{\text{g}}^{2+},\text{C}\text{r, }\text{C}{\text{o}}^{3+},\text{C}{\text{l}}^{-},\text{S}{\text{n}}^{2+},\text{T}\text{h},\text{S}\text{r}$