For for the formulas with the abbreviated names of the ions, you switch the exponents for each one, so for number 2 it would be Fe2O3 or for 6 it would be CaCl2 For the compounds, you take the abbreviated names of the ions from the periodic table and wherever the ion falls, that’s how many electrons it has and so it would need more ions to make the full shell, so for sodium chloride, since both need one, it would be NaCl or for tin (ll) fluoride, it would be SnF2
