Final answer:
The correct sentence is 'The international team will arrive on Flight 12 at Gate 48A.', as 'Flight 12' and 'Gate 48A' are proper nouns and should be capitalized.
Step-by-step explanation:
The correct sentence among the options given is: 3. The international team will arrive on Flight 12 at Gate 48A.
This is because 'Flight 12' and 'Gate 48A' are proper nouns representing a specific flight number and a specific gate number. Proper nouns are capitalized in English, which is why we capitalize the word 'Flight' and the word 'Gate' in these instances. Other entities like flight numbers and gate numbers are considered proper nouns and therefore should also be spelled with initial capital letters.
To grammar rules, when referring to specific flights and gate numbers, they should be capitalized. The same goes for any specific names, locations, or titles that are unique within their context, such as the name of a specific airport, sports team, or event.