these things are confusing, please help me fill out the blanks and correct me :

(u - is the universal set)

1. $\displaystyle \emptyset \cup \emptyset = \emptyset$ ?

2. $\displaystyle \emptyset \cap \emptyset = u$ ?

3. $\displaystyle u \cup u = $ ?

4. $\displaystyle u \cap u = $ ?

5. $\displaystyle u \cup \emptyset = u$ ?

6. $\displaystyle u \cap \emptyset = \emptyset$ ?

* - $\displaystyle if B\setminus A=A^C$ does it mean that B=u ?

thanks.