Why are halogens unreactive? A. *Halogens need one to two more electrons to fill their outer shell.
B. Halogens need three to four more electrons to fill their outer shell.
C. D. Halogens have a full outer shell of valence electrons.

Why is it important for scientists to review and repeat the work of other scientists? 1.a scientific theory must be tested three times before it is proven. 2.the scientific method only applies to repeated experiments. 3.an experiment may have had errors that the scientists didn't recognize. 4.the results of individual scientists may be influenced by bias. 5.an experiment must be performed twice before the data can be analyzed.