It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

Explanation

Green leaves contain lot of water. So, when we try to burn green leaves, water contained in the leaves cools the combustible materials (leaves), so that its temperature is brought below its ignition temperature. This prevents the burning of green leaves. In case of dry leaves, they do not contain any water. So when burning process starts, its temperature is raised drastically above its ignition temperature and the leaves catch fire easily.