Which of the following is a sign a chemical reaction has occurred?

True or false, the three major scales used to measure earthquakes are mercalli scale, richter scale and magnitude scale

What is a scientific theory? a. a scientist's guess about how something works b. the results of an experiment obtained using the scientific method c. a proven fact that will never change d. an idea that is backed by data from many sources

Determine the wavelength of the light absorbed when an electron in a hydrogen atom makes a transition from an orbital in the n=3 level to an orbital in the n=7 level.