Which of these models explain how the free electrons are present in a metal?
Electron sea model
Plum pudding model is a model of an atom in which electrons are believed to be stuck in a positively charged cloud.
Well, you know about the solar system model. Electrons revolve around positive charges, like planets around the sun.
The above models talk about a specific atom, not about the entire metal. They believe that electrons are tightly bound to a particular atom, whereas in a metal some electrons, called free electrons are not bound to a single atom but are free to move around within the boundaries of the metal under the influence of positive charges.
This can be very well depicted by the electron sea model.
Since the electrons are free to flow, we call them as "sea of electrons".
Last but not the least, everything that you don't understand is not QUANTUM Physics my friend.