Among the given options, lemon juice is the strongest acid according to the pH scale. Lemon juice has a pH range between 2 and 3, which indicates that it is acidic. NaOH (sodium hydroxide) and bleach (sodium hypochlorite) are both basic substances with pH values greater than 7. Blood, on the other hand, is slightly basic with a pH range between 7.35 and 7.45.