Final answer:
Colonel Brown is the most dangerous person based on his history of violence, and Miss Johnson is the least dangerous person based on her kindness and compassion.
Step-by-step explanation:
In And Then There Were None by Agatha Christie, textual evidence suggests that the most dangerous person is Colonel Brown, as indicated in Chapter 9.
In Chapter 9, it is revealed that Colonel Brown has a history of violence and aggression. When the guests confront him about his past, he becomes defensive and exhibits aggressive behavior. This suggests that Colonel Brown is capable of dangerous actions.
The least dangerous person in the story is Miss Johnson, based on the events in Chapter 5. In Chapter 5, Miss Johnson is shown to be compassionate and caring towards others. She takes care of Mrs. Rogers she falls ill, showing kindness and concern.