Give some stream of consciousness and then the answer. In Service Aircraft First flight Note Antonov An-225 Mriya 19881221! 21 December 1988 Generally acknowledged as the largest airplane in the world, the single Antonov An-225 is the world's heaviest aircraft ever (maximum takeoff weight greater than 640 tons) and the largest heavier-than-air aircraft (in length and wingspan) ever entering operational service. Airbus A380-800 20050427! 27 April 2005 The largest passenger aircraft ever made. Capable of carrying 850 passengers Airbus A340-600 20010423! 23 April 2001 The A340-600 has been in production since 2001, with a length of 75.30 m, the longest commercial aircraft, until surpassed by the Boeing 747-8. Antonov An-124 19820000! 26 December 1982 Was the largest mass-produced aircraft in the world until the Airbus A380 was produced. Remains the world's largest military aircraft currently in service. Antonov An-22 19650227! 27 February 1965 World's largest turboprop-powered airplane Boeing 747-8 20100208! 8 February 2010 (F variant) Lengthened version of 747 with increased wingspan. World's longest passenger aircraft at 76.4 m (0.9 m / 3 ft longer than Airbus A340) capacity of 650 passengers. Boeing 747 19690209! 9 February 1969 Highest-capacity passenger aircraft until surpassed by Airbus A380 Boeing 747 "Dreamlifter" 20060909! 9 September 2006 747 with enlarged fuselage for transporting Boeing 787 Dreamliner sub-assemblies (1,800 cubic metres ( 65,000 cu ft) ) Tupolev Maksim Gorki 19340519! 19 May 1934 Physically the largest aircraft, and heaviest land-based aircraft of the 1930s era (63 meter / 206.7 ft wingspan, 53 tonne MTOW), required eight 900 hp Mikulin V12 engines for flight Dornier Do X 19290712! 12 July 1929 Largest successful flying boat and heaviest aircraft in the world from 1929 until 1942 when the Boeing B-29 Superfortress first flew. Antonov An-2 19470831! 31 August 1947 Largest mass-produced single-engine biplane.

Based on this passage, which one is the biggest airplane in the world?
To answer this question, we should know that: In Service Aircraft First flight Note Antonov An-225 Mriya 19881221! 21 December 1988 Generally acknowledged as the largest airplane in the world, the single Antonov An-225 is the world's heaviest aircraft ever (maximum takeoff weight greater than 640 tons) and the largest heavier-than-air aircraft (in length and wingspan) ever entering operational service. Airbus A380-800 20050427! 27 April 2005 The largest passenger aircraft ever made. Capable of carrying 850 passengers Airbus A340-600 20010423! 23 April 2001 The A340-600 has been in production since 2001, with a length of 75.30 m, the longest commercial aircraft, until surpassed by the Boeing 747-8. Antonov An-124 19820000! 26 December 1982 Was the largest mass-produced aircraft in the world until the Airbus A380 was produced. Remains the world's largest military aircraft currently in service. Antonov An-22 19650227! 27 February 1965 World's largest turboprop-powered airplane Boeing 747-8 20100208! 8 February 2010 (F variant) Lengthened version of 747 with increased wingspan. World's longest passenger aircraft at 76.4 m (0.9 m / 3 ft longer than Airbus A340) capacity of 650 passengers. Boeing 747 19690209! 9 February 1969 Highest-capacity passenger aircraft until surpassed by Airbus A380 Boeing 747 "Dreamlifter" 20060909! 9 September 2006 747 with enlarged fuselage for transporting Boeing 787 Dreamliner sub-assemblies (1,800 cubic metres ( 65,000 cu ft) ) Tupolev Maksim Gorki 19340519! 19 May 1934 Physically the largest aircraft, and heaviest land-based aircraft of the 1930s era (63 meter / 206.7 ft wingspan, 53 tonne MTOW), required eight 900 hp Mikulin V12 engines for flight Dornier Do X 19290712! 12 July 1929 Largest successful flying boat and heaviest aircraft in the world from 1929 until 1942 when the Boeing B-29 Superfortress first flew. Antonov An-2 19470831! 31 August 1947 Largest mass-produced single-engine biplane.
Therefore, the answer is the single Antonov An - 225.