In this task, you are given a sentence and a question, you would be asked to create the answer which is contained in the sentence provided.
Example: Sentence: Having white fur trait would a cat most likely inherit from its parents. Question: Which trait would a cat most likely inherit from its parents?
Example solution: having white fur
Example explanation: The given output is correct as the answer provided is from the scientific fact stated

Problem: Sentence: The concentration of the hydrogen ion in a solution can be calculated when the ph is known. Question: The concentration of the hydrogen ion in a solution can be calculated when what is known?

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Solution: ph