Can a person blindfolded tell the difference between sprite and 7 up?

Assuming sample is known to be 7up but label is unreadable you have several alternatives, depending oh your resources.

1.- Just taste samples most people can tell them apart.

2.- Measure density with a suitable densimeter. The sample with the higher density will be the regular one.

3.- Same as 2 but using a densitometer. Just a fancier method.

4.- Measure refractive indexes with refractometer the sample with the higher refracrive index will corresponds to the sugar containing product.

5.- Evaporate samples to dryness and weight residues. The sample with lower residue will be the diet sample.

6.- put both samples in contact making sure they do not mix, the one that will settle on the bottom will be the regular one.