Which of the following passenger jets is the longest?

The Boeing 747-8 is the longest passenger jet among the options given. This is because the 747-8 is an extended version of the iconic Boeing 747 series, making it longer than other aircraft like the Airbus A380, Boeing 777X, and Boeing 787. The 747-8 measures around 76.3 meters (250.2 feet) in length, which allows for more passenger seating or additional cargo capacity compared to its predecessors. Its elongated structure and increased length have contributed to its title as the longest passenger jet in the list.