Explain how one and two letter chemical symbols are used to identify elements whose names begin with the same letter for example hydrogen and helium ..

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Elements are commonly named after their chemical symbols. These chemical symbols were proposed by Berzelius, using the first letter of the element's name. The exception is when two elements start with the same first letter, as is the case for Hydrogen and Helium, in this case, the two-letter chemical symbol is used and these elements are abbreviated as H and He, respectively. Other cases of these two-letter chemical symbols are Carbon and Calcium, which are abbreviated C and Ca, respectively, and many more.

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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

Less stable  hope this