Suppose that a newly discovered element called centium has three isotopes that occur in nature. these are centium-200, centium-203, and centium-209. assume that these isotopes occur in equal amounts in nature. what will be the average atomic mass of this element?

Since all the isotopes occur in the same amount, to find the average atomic mass of the element, add the three mass values together and divide the result by 3. That is, 
Average atomic mass = [200 +  203 + 209] / 3 = 612 /3 = 204.
Thus, the average atomic mass of the element is 204.

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Only one reactant yields 2 or more products. meaning you will only have 1 product and it will break down into 2 or more products. eg. h2o -> h2 + o2