Step-by-step explanation:
Molarity is the number of moles per liter of solution. Whereas number of moles is defines as mass divided by molar mass.
Therefore, Molarity =

Since, it is given that molarity is 2.80 M, volume is 500 ml or 0.5 L, and molar mass of KI is 166 g/mol.
Hence, mass =
=

= 232.4 g
Thus, mass of KI is 232.4 g which is required to prepare 5.00 X10^2 mL of a 2.80 M solution.