Solution:

• Red cabbage juice can tell if a substance is an acid or a base when added to it. It is an indicator.
• If the substance is an acid when the red cabbage juice (purple in color) is added it will turn a shade of red.
• If the substance is a base it will turn a shade of green when the juice is added to it. If the substance is neutral the cabbage juice will stay purple when added to it.
• The lemon juice will turn pink while the antacids will turn green. The aspirin also turns pink yet the tap water turns purple indicating that it is neutral.