Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: As with the hydrogen-ion concentration, the concentration of the hydroxide ion can be expressed logarithmically by the pOH. The pOH of a solution is the negative logarithm of the hydroxide-ion concentration. Answer: the poh
Output:
The negative logarithm of the hydroxide-ion concentration of a solution is called?