Answer: c. The specific heat of seawater
Explanation: Specific heat is defined as the amount of heat required to raise the temperature of unit mass of the substance by a given amount.
Concentration of ions is measured by noting the conductivity of the solution.As higher is the conductivity, higher is the concentration of ions.
Concentration of dissolved oxygen is measured by using iodometric titrations in which iodine is involved.
pH is measured by knowing the concentration of hydrogen ions.