Safe when the patch document is empty, otherwise idempotent
Idempotent but not safe, like PUT
Idempotent whenever the patch document is applied atomically
Neither safe nor idempotent, although a particular patch format can be issued in an idempotent way✓Правильный ответ
Объяснение
PATCH is defined as neither safe nor idempotent, because a patch document may describe a relative change that compounds when applied twice. The spec adds that a request can be issued so as to be idempotent, and recommends a conditional request with a strong ETag to guard against collisions; atomicity is a separate requirement and does not imply idempotency.