A scientific idea becomes valid when it is ...

tested

biased

permanent

complex

A scientific idea becomes valid when it is tested.

Explanation:

Every scientific discovery or inventions starts with the creation of idea or imagination related to the invention. Followed by the idea or the proposal for the scientific finding, the researchers should experimentally prove his proposal or assumptions. So it should be tested experimentally, to prove the validity of scientific idea. Unless and until the idea has been tested experimentally, those theoretical assumptions are of no use and it is termed to be disqualified. So the scientific idea will become valid only when it is tested and proved.