I need a little help, I've done the rest but I had trouble with these. Please explain the steps.?

Question

For metal/nonmetal combination, tell the charge on each atom in nature and determine the chemical formula of the ionic compund formed.
1.) Sr and N
2.) Ga and F
3.) Cs and O
4.) Rb and P
5.) Ca and Br
6.) Ra and I
7.) B and P
8.) Be and N
9.) Al and S
10.) B and F

Answer 1

1.) Sr3N2
2.) GaF3
3.) Cs2O
4.) Rb3P
5.) CaBr2
6.) RaI2
7.) BP
8.) Be3N2
9.) Al2S3
10.) BF3

I'm sure from these that you can work out the charges on the atoms.