An ionic compound can be formed through the existence of valency above the compound e.g NH4 which have +3 as it's ionic charge
If you can have more than 1 answer then the dependent variable is graphed on the Y-axis and and is usually used for comparison since they are usually the experiment results. If you can only have one answer then the dependent variable is graphed on the y-axis.
I believe 1 is growth and 2 is reproduction. Hope this helps.