Scale from 0 to 14 for measuring acidity or alkalinity. A pH of 7 indicates neutrality, below 7 is
acid, while above 7 is alkaline. Strong acids, such as those used in car batteries, have a pH of about 2; strong
alkalis such as sodium hydroxide have a pH of about 13.
Acidic fruits such as citrus fruits are about pH 4. Fertile soils have a pH of about 6.5 to 7, while weak alkalis such as soap have a pH of about 9 to 10.
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