Final answer:
The most favorable skeletal class for removable appliances is Class I, which indicates a normal relationship between jaws and teeth; other classes require more complex treatment.
Step-by-step explanation:
The most favorable skeletal class for removable appliances is Class I. Removable appliances are typically used in orthodontic treatment to correct dental malocclusions. Class I refers to a normal relationship between the upper and lower teeth and jaws where modification is less complex. On the other hand, Class II is characterized by an overbite with the upper jaw and teeth projecting over the lower jaw, and Class III is characterized by an underbite, with the lower jaw projecting beyond the upper jaw. Class IV does not exist in the standard classification of malocclusions, indicating that the options given include a non-existent class.
Therefore, when considering the use of removable appliances for orthodontic treatment, Class I malocclusion requires less extensive orthodontic intervention and is generally more amendable to this kind of treatment compared to the other more complex classes.