Final answer:
The concentration of dissolved oxygen in a pond at 40°C with a salinity of 5g/kg cannot be determined from the provided information alone. The 15% DO measurement indicates a value below 100% saturation, but without specific tabulated values or the application of Henry's Law, it's not possible to accurately choose from the provided answer options.
Step-by-step explanation:
Understanding Dissolved Oxygen Levels in a Pond
The question pertains to the measurement of dissolved oxygen (DO) in a pond with a known temperature and salinity. Dissolved oxygen is crucial for aquatic life and its concentration can be affected by various factors, including temperature, which in turn affects the pond's ecosystem health. If a pond's temperature is raised to 40°C and the salinity is at 5g/kg due to minerals and evaporation, measuring a 15% DO level implies that the oxygen concentration in the pond is below what would be expected at saturation.
To calculate the amount of dissolved oxygen in the pond, we would typically use a table or graph outlining the solubility of oxygen at various temperatures and salinities. However, assuming that 100% saturation at 40°C correlates with a theoretical 100% saturated DO concentration, we can use the given 15% DO measurement to estimate the concentration in the pond. For example, if 100% saturation at this temperature were equivalent to 10 g/kg, a 15% DO level would mean the pond has 1.5 g/kg of dissolved oxygen. The actual amount at 100% saturation would depend on tabulated values or calculations based on Henry's Law for the given conditions.
Given the lack of specific saturation values, the answer choices presented (6.75 g/kg, 7.5 g/kg, 8.5 g/kg, or 9.0 g/kg) cannot be accurately determined from the information provided. They assume concentrations higher than what a 15% measurement would suggest based on typical saturation levels at 40°C, indicating a potential discrepancy in the question or a need for additional data to arrive at a correct answer.