Answer:
3 is the coefficient of oxygen.
Step-by-step explanation:
Chemical equation:
CH₃OH + O₂ → CO₂ + H₂O
Balanced chemical equation:
2CH₃OH + 3O₂ → 2CO₂ + 4H₂O
The given reaction is combustion reaction. In this reaction methanol is burn in the presence of oxygen and produces carbon dioxide and water.
The balance equation show reaction also follow the law of conservation of mass.
This law was given by French chemist Antoine Lavoisier in 1789. According to this law mass of reactant and mass of product must be equal, because masses are not created or destroyed in a chemical reaction.