Answer:
Confident, sympathetic and outgoing
Step-by-step explanation:
In the Open Window short story, Nuttel is an "eccentric hypochondriac2, visiting the country, looking for someone to host him in their home, as he needed a more quieter place (he was not outgoing), so he could be more relaxed and deal with his nerve issues.
Furthermore, in the story, Nuttel is the victim of one of the characters, Vera, a fifteen-year-old girl, who tells him a fake story about the death of some of her relatives, and Nuttle easily believes what Vera says, instead of doubting of a fifteen-year-old girl. Besides, when Mrs. Sappleton enters the room, Nuttle does not ask her for further details about the tragic death, he is not kind about it, nor sympathetic about that terrible issue, as if he were too timid to even ask.
When the apparent "dead" relatives are in sight from the "Open Window", Nuttle, without saying a word, and being horrified and scared, flees the house immediately. This response is an indication of the frail condition and the lack of confident of the character, because had he been a confident, and not frail man, he would have not fleed the way he did.