Final method: Gas syringe
From my four methods I have decided that the first method was the most accurate. That method was the volume of O2 gas produced, that method was carried out by measuring 2ml of a percent of catalase, measuring 5ml of hydrogen peroxide, mixing them, waiting 20 seconds and measuring the volume of O2 gas that has been produced using a gas syringe.
This method was more accurate than the other methods because;
It was more accurate than method 2, (Time reaction takes to stop) because this method was open to many human errors, such as the fact that it is very hard to know exactly when the reaction has stopped, also the human might not stop the stopwatch directly when the reaction has stopped. The gas syringe is a lot more accurate and there is a lot less chance of there being a human error.
The first method was more accurate than the third method, (Temperature change). It was more accurate because although there is little chance of human error, the gas syringe is much more accurate than a thermometer, and lots of different things can affect the result, such as the temperature of the room.
The first method was more accurate than the fourth method, (Mass change) because again this method was open to human error, such as error while using the electric scales, as the beaker containing the solution is placed on the electric scales the human could accidentally press a wrong button causing an error. The gas syringe is also more accurate than the electric scales.