Properties of Union of Sets

Q. Three sets $A,B\&C$ such that $A\subset B,$ then $A\cup (B\cup C)=$

1. $B\cup C$
2. $A\cup C$
3. $B$

Q. For any three sets $A,B\&C;A\cup (B\cup C)=$

1. $(A\cup B)\cup C$
2. $(B\cup A)\cup C$
3. $A\cup (C\cup B)$
4. $(A\cup C)\cup B$

Q. For any set $X,X\cup \varnothing =X.$

1. False
2. True