Option 1, Zinc oxide, does not undergo thermal decomposition. Zinc oxide is a stable compound that does not break down into its constituent elements when heated.

Option 2, Silver oxide and zinc oxide, is incorrect. While silver oxide does undergo thermal decomposition, as indicated by the answer option 3, zinc oxide does not. Therefore, the correct answer cannot be option 2.

Option 3, Silver oxide, is the correct answer provided in the question. Silver oxide decomposes when heated, releasing oxygen gas and leaving behind silver as a residue. This decomposition reaction is endothermic and requires energy input in the form of heat. So, when silver oxide is heated, it breaks down into its constituent elements.

Option 4, Magnesium oxide, does not undergo thermal decomposition. Magnesium oxide is a stable compound that remains intact when heated. It does not break down into magnesium and oxygen.

In conclusion, the correct answer is option 3, Silver oxide. It is the only compound among the options that undergoes thermal decomposition when heated.