Regular language properties
True
True
False


To find the proofs, proceed as follows:


Show that any string $x \in R \cup S$ belongs to $S \cup R$, and vice versa.
Ditto 1.
Find a string $x$ that is in $(R \cup S)^*$ but not the LHS. Hint: what about $rsr$ where $r \in R, s \in S$?