2 which amoung the following measurements
the highest number of significant
containsFiqures
a) 1.23x10^-3 kg b) 1.2x10^-3 kg c)0.123×10^3kg
d) 2x 10^5 kg

PbBr₄

C₂O₆

Al₂S₃

Explanation:

Lead (IV) bromide

This is an ionic compound.  Ionic compounds do not tell you how many of each atom you have in the name.  You have to figure out how much there is based on the charges of the atoms.

The (IV) means that lead has a charge of +4.  The charge is put in parentheses since lead is a transition metal, and the charge of a transition metal can vary.  Bromine, on the other hand, is always assumed to have a charge of -1.  When making a molecular formula, you need to have enough of each atom so that the charges cancel out.

Dicarbon hexoxide

This is a covalent compound.  Covalent compounds will tell you how much of each atom you have in the name.  

Dicarbon means two carbons.  Hexoxide means six oxygens.

Aluminum sulfide

Aluminum sulfide is an ionic compound.

Aluminum has a charge of +3.  Sulfur has a charge of -2.