Final answer:
The perm solution is applied during the chemical phase of perming to disrupt disulfide bonds, making the hair pliable so it can take the shape of the perm rod, followed by a neutralizer to set the shape.
Step-by-step explanation:
During the chemical phase of perming, perm solution is applied to allow the protein chains to assume the shape of the perm rod. The perm solution contains a reducing agent which disrupts the disulfide bonds in the hair's keratin structure, allowing the hair to become pliable. Once the hair is wrapped around the perm rods in the desired shape, a neutralizer, often a dilute solution of hydrogen peroxide, is used to reform the disulfide bonds, thereby setting the hair into its new shape. This process effectively gives the hair a new permanent shape, whether curly or straight, depending on the treatment applied.