Answer:
Alkaline (or base) is a substance that is over the pH of 7. an acid is a substance that is lower than the pH of 7
When universal indicator is put into an alkaline substance it will turn blue/purple/black. If it is an acid the substance will turn red/orange/yellow
The same will happen if litmus paper is used instaed. If the paper turns blue/purple/black it means that the substance is an alkaline. If the paper turns red/orange/yellow it means that the substance is an acid
If the substance or the litmus paper turns green it means that it is neutral (It has the pH of 7)
Litmus paper and other idicators are used mostly in medical fields to check medicine is suitable for humans
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