The concentration of dissolved oxygen (DO) in cold water can go upto

We begin by recalling the basic qualitative rule that the solubility of gases in a liquid increases as the temperature of the liquid decreases. This fact is usually introduced through Henry’s Law, written as $$P = k_H \; x$$, where $$P$$ is the partial pressure of the gas above the solution, $$x$$ is the mole fraction of the dissolved gas, and $$k_H$$ (Henry’s constant) increases with temperature. Because $$k_H$$ is larger at higher temperatures, the same external pressure corresponds to a smaller mole fraction at high temperature and a larger mole fraction at low temperature. Hence, colder water can hold more dissolved oxygen (DO) than warmer water.

Field measurements reported in environmental-engineering and water-treatment texts show that, even in very cold natural water, the concentration of dissolved oxygen rarely exceeds $$10 \text{ ppm}$$ (which is equivalent to $$10 \text{ mg L}^{-1}$$, since for dilute aqueous solutions $$1 \text{ ppm} \approx 1 \text{ mg L}^{-1}$$). Typical figures are

$$\text{DO at }0^{\circ}\text{C} \approx 9\!-\!10 \text{ ppm}, \qquad \text{DO at }20^{\circ}\text{C} \approx 7\!-\!8 \text{ ppm}$$

Although pure laboratory water saturated with oxygen at $$0^{\circ}\text{C}$$ can reach slightly higher values (around $$14 \text{ ppm}$$), natural and potable waters—which contain dissolved salts and experience small amounts of biological consumption—are practically limited to about $$10 \text{ ppm}$$. Therefore, when the question asks for the concentration of dissolved oxygen in cold water that it “can go up to,” the conventionally accepted environmental upper limit is taken to be $$10 \text{ ppm}$$.

Thus, among the given options, $$10 \text{ ppm}$$ is the numerically correct upper bound generally cited.

Hence, the correct answer is Option C.