how to find ions present in compounds?

Question

I have these compounds that I don't know how to find the ions present in them:
PbF2
LiH
MnO2
Ga2I6 thats gallium2, iodine 6

Answer 1

To find ions present in compounds, equivalently, is to find ionic bonding in the compounds.
Ionic bonding is a type of electrostatic interaction between atoms which have an electronegativity difference of over 1.6 (this limit is a convention).
So you may find a periodic table of electronegativity, and easily calculate the difference in the electronegativity and make judgment whether a compound is ionic or covalent.
Further reading:
http://en.wikipedia.org/wiki/Chemical_bonds#Covalent_bond