1) Convert moles into formula units
Avogadro's number is 6.022*10^23
[tex]\text{Formula units=4.25 mol KBr}\cdot\frac{6.022\cdot10^{23}units}{1\text{ mol KBr}}=2.56\cdot10^{24}formula\text{ units KBr.}[/tex]The answer is 2.56*10^24 formula units of KBr.