How do you test a diet soda and regular to tell which is without taste or density?

It is not possible to tell the difference between a diet soda and a regular soda if both are colorless and have the same density. This is because our sense of taste is based on the chemical composition of the food or drink, and our sense of density is based on the mass and volume of the object. If both sodas have the same chemical composition and the same mass and volume, then they will taste and feel exactly the same.