The compound #"Pb"("OH"_2)# contains two ions:
- The cation #"Pb"^(2+)#, and
- The anion #"OH"^-#.
#"Pb"# (lead) is a transition metal and has more than one possible oxidation state. Hence by the IUPAC naming law, it would be necessary to indicate the oxidation state of the element using Roman numerals contained in brackets. [1]
The #"Pb"^(2+)# ion has an ionic charge of #2+#, meaning that it has #2# fewer electrons than protons. Thus its oxidation charge would be #+2#, which corresponds to the systematic name #"Lead" ("II")#.
The anion #"OH"^-# is the #"hydroxide"# ion. Combining the name of the cation with that of the anion would give the name of this ionic compound.
Reference
[1] IUPAC nomenclature of inorganic chemistry, the English Wikipedia, https://en.wikipedia.org/wiki/IUPAC_nomenclature_of_inorganic_chemistry
