Answer:
CLEANER
Explanation:
Independent variable is the variable in an experiment that is changed or manipulated by the experimenter in order to bring about a measurable response.
In this question, Marie notices that the current cleaner she is using on her shower is not cutting through the hard water build-up that has accumulated. She decides to purchase 3 other cleaners to see if one of them will do a better job of cutting through the stains. The CLEANERS being changed in this experiment is the INDEPENDENT VARIABLE.
By decreasing n we can increase presure because decrease in n will shift equilibrium to either forward or reverse direction
