contestada

Which of the following are decomposition reactions? *
1. CH4 (g) + O2(g) → CO2 (g) + H20 (1)
2. Cao (s) + CO2(g) → CaCO3 (s)
3. Mg (s) + O2 (g) – Mgo (s)
4. POCO3 (s) – Pbo (s) + CO> (9)