Which of the conversion factors below is the "center piece" or middle step of every stoichiometry problem? a) molar volume b) molar mass c) mole ratio d) avogadro's number

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The Mole Ratio is the "center piece" of every stoichiometry problem

The proportions in a chemical reaction are given in moles, so we can't use grams to make calculations. A typical stoichiometry problem involves knowing the grams of a reagent and using the molar mass (g/mol) to calculate the moles of that reagent. 

Then comes the central part of every stoichiometry problem, which involves converting the moles of one substance into the moles of another. This is done by using the mole ratio, which is the relationship that exists between the moles of two substances that are involved in a chemical reaction and allows us to convert these units. 

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They are like other investigations? say there was a murder u have to do blood test and finger prints which run through a lab.