Answer
Red : Potassium sulfide. $(K_2S)$
Green: Strontium iodide $(SrI_2)$
Blue: Gallium oxide $(Ga_2O_3)$
Work Step by Step
1. Use the periodic table to get the name of the metals:
Red: Potassium
Green: Strontium
Blue: Gallium
2. Use the figure 2.15 (Page 61) to find the name of the nonmetal ions:
Red: Sulfide.
Green: Iodide.
Blue: Oxide.
3. To write its likely formula, multiply each number of atoms by the charge of its pair. (Use figure 2.15):
(a) $K_2S$
** Since sulfide has a charge of $2-$, we use 2 potassium ions.
(b) $SrI_2$
(c) $Ga_2O_3$
