Final answer:
The tuba is the instrument featured in the Tuba mirum section from Mozart's Requiem.
Step-by-step explanation:
The instrument featured in dialogue with the bass singer in the Tuba mirum section from Mozart's Requiem is the tuba. The tuba is a large brass instrument that produces deep and powerful sound. It is commonly used in orchestras and brass bands to provide the bassline and support the low register of the ensemble.