How is the number of moles of an element determined from a known mass? A. The known mass is divided by Avogadro's number to get moles.
B. The mass of 1 mole of the element is used as a conversion factor to convert grams to moles.
C. The atomic number is used as a conversion factor to convert grams to moles.
D. The known massis multiplied by Avogadro's number to get moles.

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a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o