Answer:
To find the percentage by volume of alcohol, we need to divide the volume of alcohol by the total volume of the solution, then multiply by 100%:
Volume of alcohol = 19 mL
Total volume of solution = 19 mL + 31 mL = 50 mL
Percentage by volume of alcohol = (19/50) x 100% = 38%
Therefore, the percentage by volume of alcohol in the solution is 38%.