What is an acid and what is an alkali?
The answer to your question really depends upon the level of answer that you need. At a most basic level (excuse the chemistry pun!), acids taste sour and alkalis taste soapy. Or you could define them as having pH values below or above 7 respectively. Or you could talk about the release or acceptance of protons in solution. If you’d like to refine your question to the level you are at, I will amend the answer accordingly.
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