What is true about the relative concentrations of hydrogen ions or hydroxide ions in an acidic solution?

a
hydrogen-concentration is less
b
hydroxide-ion concentration is greater
c
the concentrations are equal
d
hydroxide-ion concentration is less

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.