What happens to the majority of energy at each trophic level in an ecosystem?
Most energy at each trophic level is lost as heat during respiration, following the second law of thermodynamics. This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.