How do Mahler's symphonies primarily differ from those of Haydn?

Mahler's symphonies are characterized by their thick orchestration, which distinguishes them from those of Haydn. Mahler expanded the orchestra significantly, incorporating a wide variety of instruments, including brass, woodwinds, percussion, and strings, often in large numbers. This richer and more complex orchestral texture allows for greater emotional expressiveness and a broader range of sound dynamics in Mahler's works.

In contrast, Haydn's symphonies, rooted in the Classical period, generally feature a smaller orchestra and simpler textures. While Haydn's orchestrations are masterful in their own right, they do not exhibit the same level of instrumental diversity and complexity that one finds in Mahler's compositions.

The other options illustrate characteristics that do not accurately represent Mahler's symphonies when compared to Haydn's. For example, Mahler's symphonies are not shorter; in fact, they are often longer and more sprawling. Additionally, while Mahler's works are predominantly orchestral, he also composed vocal symphonies and song cycles that incorporate human voice, which is a notable feature lacking in Haydn's purely orchestral symphonic style. Lastly, Mahler is renowned for his thematic diversity, often weaving several themes throughout a single movement