How do I find the charge of the 1st listed metal?
HgCl2
PbO2
Cu(OH)2
Cr2O3
Fe3(PO4)2
For HgCl2, you know Cl is -1, there are two of them for a total of -2. Since HgCl2 must be zero, what must Hg be for that to happen? Hg must be +2 so that +2 and -2 = 0.
PbO2. O is -2, there are two of them for a total of -4. So Pb must be +4 so that +4 and -4 = 0.
The others are done the same way. OH is -1.
PO4 is -3.