Answer: c) The concentration of a single major constituent can be measured to determine the total salinity of a water sample.
Explanation: The law of constant proportions is also known as Proust’s law or as the law of definite proportions. It states that chemical compounds are consists of elements that are present in a fixed ratio by mass.
No matter how much the salinity increases or decreases in the ocean, the number of ions proportional to each other remains constant.