Q.9 It is difficult to burn a heap of green leaves but dry leaves catch fire easily. Explain.

A heap of green leaves has a lot of water content which makes their burning a long process. As they have high ignition temperature, hence they does not catch fire easily.

The ignition temperature of a substance is the least temperature at which the substance starts combustion.

As dry leaves have less water content or no water content, hence their ignition temperature is low. As a result they catch fire easily.