Final answer:
The concentration can be calculated only with TISAB.
Step-by-step explanation:
The correct answer is B) The concentration can be calculated only with TISAB.
In this question, TISAB stands for Total Ionic Strength Adjustment Buffer, which is used in the determination of fluoride ion concentration. TISAB helps to maintain the pH and ionic strength of the sample, allowing for accurate measurements.
Without TISAB, interference from other ions in the sample can affect the measurement of fluoride concentration. Therefore, TISAB is necessary to obtain an accurate concentration of F⁻ in the unknown sample.