Explanation:

- Human blood: It has a pH around 7.4, which is slightly alkaline. It's essential to maintain this pH for proper bodily functions.

- Milk of magnesia: This is an alkaline substance with a pH between 10 and 11. It's often used as an antacid.

- Lemon juice: This liquid is acidic, with a pH around 2 to 3. It's commonly consumed in beverages and cooking.

- Orange juice: Similar to lemon juice, orange juice is also acidic with a pH around 3 to 4.

Milk of magnesia has the highest pH out of the options.