Question

Which two elements most commonly affect the mood of a story?

Answer 1

Conflict and I don’t know the other

Answer 2

Since it's the attitude of the narrator, tonewon't change as often as mood can. Style is the third element used for creating or changing the feel of a story or scene, though it's a bit different from tone and mood because it's used to affect and create the other two elements.
Conflict also affects the mood.