A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue?
Lemon juice
Vinegar
Common salt
An antacid
Steps: Yellowish-orange indicates acidic to neutral pH. An antacid is basic and will raise pH to alkaline (greenish-blue). Lemon juice and vinegar are acidic; common salt is neutral.