You are on a field trip and are recording the amount of mass in a volume of water. what are you measuring? a) the concentration of bacteria in seawater b) the concentration of dissolved oxygen in seawater c) the concentration of salt in seawater d) the density of seawater

The correct option is "D", "The density of seawater".
As you are measuring the amount of mass in a volume of water and if we look at the definition of density, it is the mass per unit volume.
D = m/v
where m is the mass of an object and v is the volume.
Thus, d is the correct option.

Fungi is were it belongs