Answer
There are 6.67 $\times$ $10^{30}$ molecules in a pool
Work Step by Step
Molecules of water = (cubic meters) $\times$ $\frac{grams}{(cubic meters)}$ $\times$ $\frac{molecules}{grams}$
= (200$m^{3}$) $\times$ $\frac{9.98\times10^{5} grams}{(1 m^{3})}$ $\times$ $\frac{3.34\times10^{22}molecules}{1 gram}$
= 6.67 $\times$ $10^{30}$ molecules
