The final isotope that is produced after flerovium-289 undergoes decay by the sequential decay of two alpha particles is Lead-281.
Flerovium-289 is an unstable isotope that is known to decay through alpha decay, which involves the emission of an alpha particle (a helium nucleus) from the nucleus of the atom. An alpha particle is made up of two protons and two neutrons. When an atom undergoes alpha decay, it loses two protons and two neutrons from its nucleus, which reduces its atomic number by 2 and its mass number by 4.
In the case of flerovium-289, the atomic number of flerovium is 114, after emitting 2 alpha particles, the atomic number would be 110, which corresponds to the element lead. The mass number of flerovium-289 is 289, after emitting 2 alpha particles the mass number would be 285, which corresponds to the isotope of lead-281.
Therefore, the final isotope that is produced after flerovium-289 undergoes decay by the sequential decay of two alpha particles is Lead-281.