Liquid water boiling in an open pan on a stove is our system. Is the system open or closed? What boundary transfers are happening? Is the system at steady state?

It's an open system, tranfering heat through a rigid, diathermal wall and matter through an imaginary and permeable wall, and it is not at steady state.

Explanation:

An open system is that that interacts with its surroundings exchanging energy and matter. In an open pan with boiling water you have an open system because steam (matter) is leaving the system, as well as heat (energy) through the pan/stove. A boundary is what separates the system from its surroundings, there are many types of boundaries, based on how they transfer energy they can be diathermal (conducting heat) or adiabatic (insulating), on their rigidity they can be rigid, flexible, imaginary or movable and based on their permeability. For the system described we have an imaginary boundary on top that is also permeable allowing matter to go out or in the system, and another wall (the stove/pan itself that is rigid and impermeable avoiding the loss of matter and diathermal, allowing the conduction of heat. It is said that a system is at a steady state when the variables that define that system remain constant over time. In an open pan, you can't fully control those variables, you'll have matter and energy scaping from it with no way to regulate it.

I hope you find interesting and useful this information! good luck!