Acids have a sour taste and change the colour of blue litmus to __________, whereas bases have a bitter taste and change the colour of red litmus to _________.

Bases turn red litmus paper blue, and they have a pH greater than 7, while acids turn blue litmus paper red and have a pH less than 7.

The pH scale is a measure of the acidity or basicity of a solution, with values ranging from 0 to 14. A pH of 7 is neutral, meaning the solution is neither acidic nor basic. A pH below 7 indicates an acidic solution, while a pH above 7 indicates a basic solution.

Common examples of bases include household cleaning products such as ammonia, baking soda, and lye. 

Common examples of acids include lemon juice, vinegar, and hydrochloric acid.