It is Rio.
bra
I guess you mean Rio, which comes from Rio de Janeiro the full name of the city. It's hard to shorten Lima or Brasilia any further. Other cities could be Salvador or Aracuja
Brasília is a city in Brazil. It is also the capital of Brazil.
There is a city in Brazil with the name Uberaba.
favela
Brasilia
Brazil has many airports. It depends on what city or location you are asking about.
· Porto Alegre is the name of a city in Brazil
The shortened name for oxygen is O2.
Xanxerê
Its São Paulo. The capital (and largest city) has the same name of the state. Same thing happens with the Rio de Janeiro state, where the capital and largest city also has the same name as the state.
I'm not sure whether the City of SOWETO, next to Johannesburg, SA qualifies as your answer because, the name seems now to have been permanently, not often, 'shortened.' It was originally SOuthWEst TOwnships, and that got compressed into Soweto.