Proof of Return

In order to apply for the VISA it is necessary to provide proof of a return or onward travel.
Would it be ok if I bought a one way ticket to RIO & a refundable ticket from RIO to Buenos Aires?
Would is the best way around this proof of return/onward travel?

I would make sure to have proofs of both tickets (the ticket for Argentina with you!) when you travel.  My friend who is french and has a permenant visa in Brazil even had problems with a one way ticket.  When she was boarding the plane, they refused to let her on (from Paris).  She called the Federal Police to confirm she was in fact allowed to board (how the hell she got them on the phone is amazing people don't always pick up Brazil).  Plus I would definitely confirm with the consulate of Brazil in your country.  No one here on this website can give you a for sure answer--only them.