Classical music era

[MURKY]

Does anyone know what feature of the orchestra was dropped out of use by the classical era in music?

[Clanad]

The Classical Period for orchestra lasted from ca. 1750 to about 1825. Prior to that time, the compositions were highly ornamental and to the classicist sounded, well... cluttered. During the Classical Period, compostions became much more structured and precise. More formal, if you will. The style period preceding Classical was and is known as Baroque...
Since your question has a certain odor reminicscent of a homework assignment, perhaps you could study this attachment for more information...

http://dorakmt.tripod.com/music/orchest.html

Best of luck on the grade!