Final answer:
The question seems to be asking about hairdressing techniques rather than bicep curls. The proper answer is an off-base curl, which allows for greater hair mobility and creates a softer look.
Step-by-step explanation:
The type of curl that is placed completely off base and allows for the greatest mobility is the off-base curl. The options listed in the question (Concentration curl, Preacher curl, Hammer curl, Spider curl) are all types of bicep curls, not hair curls. An off-base curl in hairdressing is a curl that is wound on a roller that sits completely off the base of the section, producing a curl with the least volume and the most mobility compared to on-base or half-base curls.
This technique allows the hair to move more freely and is ideal for creating a softer, more relaxed hairstyle. In relation to hair curls, none of the options provided correctly answer the question, since they refer to different exercises targeting the biceps rather than hair styling.