Question

choose the symbol for the barium cation. select all that apply
a $\ce{br^-}$
b $\ce{ba^{2+}}$
c $\ce{ba^{++}}$
d $\ce{bro3^-}$

Explanation:

Barium is a group 2 element, so it forms a +2 cation. The standard notation for a cation with a +2 charge places the number before the sign as a superscript ($\text{Ba}^{2+}$). While $\text{Ba}^{++}$ is an informal way to write the same charge, the IUPAC-preferred and standard scientific notation is $\text{Ba}^{2+}$. $\text{Br}^-$ is a bromide anion, and $\text{BrO}_3^-$ is a bromate anion, neither of which are barium cations.

Answer:

b. $\text{Ba}^{2+}$