Final answer:
Milk has the lowest [H+] concentration but is still considered an acid.
Step-by-step explanation:
According to the pH scale, substances with lower pH values are considered more acidic. Based on the given pH values, the substance with the lowest [H+] concentration but still considered an acid is:
- Milk, urine, saliva with a pH range of 6.3-6.6.
In this case, milk falls within the pH range of 6.3-6.6, which is lower than the pH values of blood (7.4), gastric fluid (typically below 2), and household lye (pH 13.5).