The acidity and the basicity are expressed by pH (the negative logarithm of the hydronium ion activity).
The acidity or basicity are expressed by pH (the negative logarithm of the activity of hydronium ion).
PH value
Electricity
2, digits in marina and icity in avenues. Maybe more though
There is no prefix in electricity. The suffix is -icity, made up of the adjective suffix -ic and the Latin noun suffix -ity.