Question to you: What must a chemical reaction overcome before starting?
Options:
- (A) PV=nRT
- (B) heat or cold
- (C) reactants
- (D) energy barrier
- (E) Dehydration
- (F) harmful substances
- (G) resistance
- (H) temperature.
Let's reason step-by-step:
All chemical reactions require activation energy to get started. Activation energy is required to overcome the energy barrier. All chemical reactions must first overcome the energy barrier. Final answer: (D).