Which of the following airport codes represents Portland, Oregon?

The airport code that represents Portland, Oregon, is PDX. This code is derived from a phonetic representation of Portland International Airport's name. Each airport is assigned a unique three-letter code by the International Air Transport Association (IATA), which helps in identifying them easily in flight itineraries, baggage tags, and other travel-related communications.

In this case, PDX captures the essence of Portland through its initials, making it memorable and relevant to travelers. The other options represent different airports in various locations: MCO is for Orlando International Airport in Florida, SFO is for San Francisco International Airport in California, and DCA is for Ronald Reagan Washington National Airport in Washington, D.C. Each of these codes pertains to airports that are distinctly different from Portland, further emphasizing why PDX is the correct answer for Portland, Oregon.