The percent composition of FeO, or iron(II) oxide, can be calculated by determining the mass percent of iron (Fe) and oxygen (O) present in the compound.

1. Calculate the molar mass of FeO:

- Molar mass of Fe = 55.845 g/mol

- Molar mass of O = 16.00 g/mol

Molar mass of FeO = (1 x 55.845 g/mol) + (1 x 16.00 g/mol) = 71.845 g/mol

2. Determine the mass of each element in 1 mole of FeO:

- Mass of Fe in 1 mole of FeO = 55.845 g/mol

- Mass of O in 1 mole of FeO = 16.00 g/mol

3. Calculate the percent composition:

- Percent composition of Fe = (Mass of Fe / Molar mass of FeO) * 100%

= (55.845 g/mol / 71.845 g/mol) * 100%

= 77.85%

- Percent composition of O = (Mass of O / Molar mass of FeO) * 100%

= (16.00 g/mol / 71.845 g/mol) * 100%

= 22.15%

Therefore, the percent composition of FeO is approximately 77.85% Fe and 22.15% O.