What could he have done to increase the validity of his data? Reduce the number of plants. Remove the 1 hour group. Add a 0 hours control. Measure the oxygen in liters.
The best and most correct answer among the choices provided by the question is the fourth choice. The procedure that could be done to increase the validity is to measure the oxygen in liters. I hope my answer has come to your help. God bless and have a nice day ahead!
