The formula for the illegal drug cocaine is c17h21no4 (303.39 g/mol). what is the percentage of hydrogen in the compound? 21.09% 4.618% 67.30% 6.991% 3.959%

Molar mass is the sum of the products of molar masses of individual elements by the number of atoms of the element in the compound.
molar mass of H - 1.01 g
number of H atoms - 21 H atoms 
therefore mass of H in 1 mol of compound - 1.01 g x 21 = 21.21 g
the molar mass of the compound - 303.39 g/mol 
H composition percentage = 
            composition percentage = 21.21 g/mol /303.39 g/mol x 100%
H composition percentage = 6.991 %

therefore answer is 6.99 %

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