researcher recruits participants for an experiment by posting an announcement in the psychology department asking for volunteers. What kind of sampling is being used?

Simple Random Sampling

Explanation:

Sampling is the process of drawing a small group of representative people from population.

Random Sampling is when all the units of population have equal chance of being chosen as a sample.

Simple Random sampling is choosing a subset randomly from the entire set.

Researcher recruiting participants for experiment by posting announcement in psychology department, asking for volunteers. It is a simple random sampling as sample is randomly drawn by invitation to volunteer from the population of all people in psychological department.