Final answer:
Haydn's masterworks in the symphonic genre are his last set of twelve symphonies, known as the London Symphonies.
Step-by-step explanation:
The correct answer to the question is c. London Symphonies. Haydn's masterworks in the symphonic genre are his last set of twelve symphonies, which are commonly known as the London Symphonies. These symphonies were composed during Haydn's second visit to London between 1791 and 1795, and they represent some of his finest and most mature compositions in the symphonic form.