Final answer:
A veterinary technician may legally perform the task of administering isoflurane, while tasks like canine castration, diagnosing feline epilepsy, and prescribing ampicillin are duties that typically fall under the responsibility of a licensed veterinarian.
Step-by-step explanation:
Among the tasks listed, a veterinary technician may legally perform administering isoflurane, which is an anesthetic agent commonly used in veterinary medicine. Veterinary technicians are trained to assist veterinarians in various procedures and often handle tasks related to patient care and anesthesia under the supervision of a licensed veterinarian. Tasks such as canine castration, diagnosing feline epilepsy, and prescribing ampicillin, which include performing surgery, making a diagnosis, and prescribing medication, respectively, are typically the responsibility of a veterinarian and are not within the legal scope of practice for veterinary technicians.