In this question, we have to find the percent by mass of NaHCO3 dissolved in water, and we can do that by using the percent by mass formula, which is:
%mass = mass of the solute/mass of the solution
We have:
20 grams of NaHCO3, this will be the solute
600 grams of H2O, +20 grams of the NaHCO3 = 620 grams, this will be the solution
Now we add the values into the formula:
%mass = 20/620 = 0.032
Therefore the percent by mass of NaHCO3 in water in this question will be 3.2%