# What are the formulae of barium nitrate, strontium sulfide, and beryllium iodide?

$\text{Barium nitrate}$ $=$ $B a {\left(N {O}_{3}\right)}_{2}$; $\text{strontium sulfide}$ $=$ $S r S$; $\text{Beryllium iodide}$ $=$ $B e {I}_{2}$.
So you've got them all right save for $\text{Barium nitrate}$ $=$ $B a {\left(N {O}_{3}\right)}_{2}$. Barium is a Group 2 metal, and commonly forms the $B {a}^{2 +}$ ion; with the uninegative nitrate ion, $N {O}_{3}^{-}$, it will form an electrically neutral salt with 2 equiv anion and 1 equiv of metal ion, i.e. $B {a}^{2 +} {\left(N {O}_{3}^{-}\right)}_{2}$. Capisce?