Question

Ignition temperature of ___________ is lower than that of wood.

Answer 1

Hint: The lowest temperature at which a combustible substance when heated (as in a bath of molten metal) takes fire in air and continues to burn is called ignition temperature. It is also known as autogenous ignition temperature.

Complete answer:
Ignition temperature is not always a unique property of a fuel because it is dependent on several other factors such as oxygen, partial pressure, particle size, rate of heating, and a particle's thermal surroundings.
The ignition temperature of wood is affected by how long it is exposed to heat. At 250–300 degrees Celsius, wood usually ignites. The wood begins to carbonise at a rate of 0.8 mm per minute after ignition. In a solid wood product, fire spreads slowly because the layer of carbon created protects the wood and slows the increase in temperature of the wood's inner parts, slowing the spread of the fire.
The ignition temperature is generally lower for higher volatile matter content fuel. Because biomass particles have a higher volatile matter content than coal, they have a significantly lower ignition temperature.
Gasoline (Petrol) has an auto-ignition temperature of $536^oF$.
Petrol catches fire at very low temperature and thus has low ignition temperature, while wood and coal have high ignition temperature.
Hence, the ignition temperature of petrol is lower than that of wood.

Note:
If a fuel has very low ignition temperature then exothermic chemical reactions can take place even at room temperature, but the reaction rate, being an exponential function of temperature, is very slow at low temperatures. The heat loss from the fuel, on the other hand, is a linear function of its temperature.