Which characteristic should a good scientific question have?

it should lead to a hypothesis that is not testable.
it should have a very broad focus with many variables.
it should repeat a question that the researcher has answered before.
it should be based on observations instead of just imagination.

The right option is; It should be based on observations instead of just imagination

Asking a scientific question is the first part of the scientific method. A good scientific question should be based on observations of a matter of interest and not just imagination, and it should have some actual answers. Also, a good scientific question should be testable through an experiment and should lead to a hypothesis that is confirmable.