Which compound has the highest percent com­position by mass of strontium?
(1) src12 (2) sri2 (3) sro (4) srs

option (3) SrO, with 84.56%

Explanation:

You have to calculate the mass of strontium and the mass of the compound, for each of the four compounds, and compute the percent:

percent of strontium = (mass of strontium / mass of the chemical formula) × 100 %.

These are the atomic masses of the elements that you have to use:

Atomic mass of Sr: 87.62 g/mol

Atomic mass of Cl: 35.453 g/mol

Atomic mass of I: 126.904 g/mol

Atomic mass of O: 15.999 g/mol

Atomic mass of S: 32.065 g/mol

(1) SrCl₂:

i) mass of Sr: 87.62 g/mol

ii) mass of Cl₂: 2×35.453 g/mol = 70.906 g/mol

iii) mass of SrCl₂: 87.62 g/mol + 70.906 g/mol = 158.526 g/mol

iv) Sr % = [87.62 / 158.526 ] × 100 = 55.27%

(2) SrI₂

Following the same procedure:

i) Sr % = [87.62 / (87.62 + 2× 126.904) ] × 100 = 25.66%

(3) SrO

i) Sr % = [87.62 / (87.62 + 15.999) ] × 100 = 84.56%

(4) SrS

i) Sr % = [87.62 / (87.62 + 32.065) ] × 100 = 73.21%

B.Chlorine

D. They are very reactive