Question 4: some of the energy is being used to change the state of some of the water.
At some places in the pot, usually at the bottom right next to the fire, water at 100°C is changing to steam at 100°C. That "phase change" takes energy, and the temperature doesn't change.
Question 5: I have no questions about this. I understand it well enough for the time being. I am confused by many things, but a pot of boiling water is not one of them. I have no important feedback at this time, but please check back with me in a week or two. Thank you.
