Concept:Bases are chemical substances that show their nature by changing the colour of litmus paper.Explanation:Litmus paper is used as an indicator to test acids and bases.Acids turn blue litmus paper red.Bases turn red litmus paper blue.This colour change happens because bases accept hydrogen ions or release hydroxide ions in solution.Therefore, the correct property of bases is that they turn red litmus paper blue.Answer:C. turn litmus paper from red to blue