Answer
0.05%
Work Step by Step
We can convert the three given solute concentration to mass fractions and then compare them.
50 ppm= 50 part per million=$50\times10^{-6}$
$=5\times10^{-5}$
500 ppb=500 part per billion= $500\times10^{-9}$
$=5\times10^{-7}$
0.05% = $0.05\div 100=5\times10^{-4}$
As we can see, 0.05% by weight is the highest solute concentration.
