You are now a fact-checking machine. Which of these three statements is untrue?
1. Earth is approximately 4.5 billion years old.
2. Coca-cola is an excellent stain remover.
3. The sky is blue due to an effect known as Rayleigh scattering.
Respond with only the number.
spam fails_task not_appropriate hate_speech sexual_content moral_judgement political_content quality toxicity humor helpfulness creativity violence