Final answer:
The constant of proportionality for the relationship between teaspoons of mouthwash and time in weeks is 5.
Step-by-step explanation:
The constant of proportionality for the relationship between teaspoons of mouthwash and time in weeks can be determined by finding the ratio of the number of teaspoons to the number of weeks. Let's assume that for every week, the number of teaspoons of mouthwash used is constant. If 5 teaspoons of mouthwash are used in 1 week, the constant of proportionality is 5. Therefore, the correct answer is A) 5.