Which of the following liquids has the highest pH?

Milk of magnesia

The correct answer is option 3. Milk of magnesia.

Among the options provided, the liquid with the highest pH is Milk of magnesia.

Milk of magnesia is a suspension of magnesium hydroxide in water. Magnesium hydroxide is a strong base, and it typically has a pH greater than 7, making it alkaline. Orange juice, lemon juice, and human blood are more acidic in nature, with lemon juice being particularly acidic due to citric acid.