Why does water boil at a lower temperature at reduced pressure?

Question

Physics

Why does water boil at a lower temperature at reduced pressure?
And what is the relationship between vacuum and vacuum?
I noticed that most pumps usually discharge air to 0.93, what is the reason for this?
And how does the fullness of the container affect the process?
For example, when is our container 2/3 filled and when is it 1/3 filled with water?
What is the effect of this difference between water and air, while maintaining their level and the same degree of rarefaction?

Answer 1

https://www.youtube.com/watch?v=UMld6gSiQS8