What compound would form between lead(II) and oxygen?
The ionic compound lead(II)oxide with the formula PbO will form from the lead(II) ion and oxygen.
When metallic lead reacts with oxygen it is oxidized to Pb2+ and oxygen is reduced to O2-, and the charges of +2 and -2 result in a one to one ratio of ions in the formula.
To find the formula of an ionic compound, you need to know the charges of the two ions. In this case you were given the name lead(II) which tells you that it's Pb2+. Transition metals that can form more than one positive ion have a Roman numeral that specifies the charge, in this case II = +2.
Oxygen always forms a -2 ion. A representative element's ionic charge can usually be determined by its chemical family: +1 for Group 1, +2 for Group 2, +3 for B and Al, -3 for nitrogen and phosphorous, -2 for the oxygen family and -1 for the Halogens (fluorine family).
Once you know the charges, use subscripts to balance the positive and negative charge so that the net charge on the molecule is zero. In this case the subscripts are 1.