Answer:
253 mmol
Explanation:
The solubility is calculated by the given equation:
S(g) = k P(g)
where k = 1.3 x 10⁻³ mol/L-atm
and P(g) = 0.21 (705 mmHg/760 mmHg/atm) = 0.195 atm
Notice the pressure is converted to atm because Henry´s constant is in units of atmospheres , and also we multiplied by 0.21 oxygen composition.
S(g) = 1.3 x 10⁻³ mol/L-atm x 1000 mmol/mol x 0.195 atm x =253 mmol
Here we did multiply by the factor 1000 mmol/mol since the mmol concentration is required in the answer.