What is the concentration of O2 (g), in parts per million, in a solution that contains 0.008 gram of O2 (g) dissolved in 1000. grams of H2O (l) ?

concentration of O₂ dissolved in H₂O can be written as ppm

ppm stands for parts per million - mg/kg

the amount of mg in 1 kg of solution

the mass of O₂ - 0.008 g

1000 mg equivalent to 1 g

therefore mass of O₂ in mg - 0.008 g x 1000 mg/g = 8 mg

the mass of water is 1000 g

1000 g is equivalent to 1 kg

mass of water in kg - 1000 g / 1000 g/kg = 1 kg

there's 8 mg of O₂ in 1 kg of water

therefore concentration of O₂ is - 8 mg/kg

also can be written as 8 ppm

answer is 8 ppm