Final answer:
The dependent variable in the activity where rocks were placed in acid solutions to measure mass loss is the amount of rock mass dissolved by the acid.
Step-by-step explanation:
In the lab activity described, the dependent variable is the mass of the rock that is dissolved by the acid solution. This is because the dependent variable is what the experimenter measures or observes in response to the manipulation of the independent variable. In this case, the independent variable could be the type of rock or the type of acid solution used. The loss of rock mass in different acid solutions is what is being measured after a week, and it is dependent on the type of rock's reaction to the acid.
It's essential to clearly define the dependent and independent variables in an experiment to better understand the cause-and-effect relationship. The dependent variable is affected by the independent variable, which is the factor that the scientist changes on purpose to see if it has an effect.