Which compound has the highest precent composition by mass of strontium?

A) SrCl2

B) SrI2

C) SrO

D) SrS

First find the molar masses of all of the compounds:

SrCl2 = 158.53g/mol

SrI2 = 341.43g/mol

SrO = 103.62g/mol

SrS = 119.68g/mo

Then find the molar mass of Sr in each of the compounds. Since there is only one Sr in every compound, the mass will be the same: 87.62g/mol Sr

Now divide the molar mass of Sr by each of compounds' masses:

SrCl2 = (87.62) / (158.53) = 0.553

SrI2 = (87.62) / (341.43) = 0.257

SrO = (87.62) / (103.62) = 0.846

SrS = (87.62) / (119.68) = 0.732

Now multiply each of the results by 100 to get the percent composition of Sr by mass:

(0.553) (100) = 55.3% Sr in SrCl2

(0.257) (100) = 25.7% Sr in SrI2

(0.846) (100) = 84.6% Sr in SrO

(0.732) (100) = 73.2% Sr in SrS

Thus SrO has the highest percent composition by mass of Sr