Final answer:
The instrument heard in the arrangement is an organ.
Step-by-step explanation:
The instrument heard in this arrangement of Bach's Fugue in G Minor by Leopold Stokowski is indeed an organ. The powerful and rich sound of the organ is a prominent feature of this arrangement, adding to the grandeur and intensity of the music. Stokowski's arrangement showcases the versatility and expressiveness of the organ as it captures the complexity and counterpoint of Bach's fugue.