Final answer:
Water left in the end papers dilutes the neutralizer, thereby reducing its effectiveness in reforming the disulfide bonds necessary for maintaining the hair's curl pattern after a perm.
Step-by-step explanation:
When water is left in the end papers after rinsing the perm solution, and it dilutes the neutralizer, the correct answer is C) Reduces the effectiveness of the neutralizer. This is because the neutralizer's role is to reform the disulfide bonds in the hair that were broken by the perm solution to create the new curl pattern. If the neutralizer is diluted with water, its concentration is reduced, which may lead to a weaker neutralizing process and consequently less effective curl formation.