5D.7 The minimum mass concentration of oxygen required for fish life is 4 mg.L-!. (a) Assume the density of lake water to be 1.00 g ml, and express this concentration in parts per million (which is equivalent to milligrams of O2 per kilogram of water, mg.kg :). (b) What is the minimum partial pressure of Oz that would supply the minimum mass concentration of oxygen in water to support fish life at 20C? (c) What is the minimum atmo- spheric pressure that would give this partial pressure, assuming that oxygen exerts about 21% of the atmospheric pressure? See Table 5D.2