When the temperature falls below the ignition temperature of a burning substance, it gets extinguished. This is because the ignition temperature is the minimum temperature at which the substance can continue to burn.

Explanation:

Ignition Temperature:
- The ignition temperature is the minimum temperature at which a substance can start or continue to burn.
- Different substances have different ignition temperatures. For example, wood has an ignition temperature of around 300 degrees Celsius, while gasoline has an ignition temperature of around -45 degrees Celsius.
- Once a substance reaches its ignition temperature, it undergoes a chemical reaction called combustion, where it reacts with oxygen to produce heat and light.

Extinguishing the Burning Substance:
- When the temperature falls below the ignition temperature of a burning substance, the combustion reaction cannot be sustained.
- This is because the reactants need a certain amount of energy (in the form of heat) to initiate and continue the combustion process.
- If the temperature falls below this threshold, there is not enough heat energy available to keep the reaction going, and the flame will go out.

Effect of Temperature on Combustion:
- At temperatures below the ignition temperature, the reactants may still be present, but they are not able to react with oxygen to sustain the combustion process.
- The lack of heat energy prevents the reactants from reaching their activation energy, which is the minimum energy required to start a chemical reaction.
- As a result, the burning substance will stop burning and the flame will be extinguished.

Examples:
- If a candle flame is exposed to a cold breeze, the temperature around the flame may decrease.
- If the temperature drops below the ignition temperature of the candle wax, the flame will go out.
- Similarly, if a wood fire is not provided with enough fuel or heat, the temperature may fall below the ignition temperature of the wood, causing the fire to die down.

Therefore, when the temperature falls below the ignition temperature of a burning substance, the combustion process cannot be sustained, and the substance gets extinguished. This is why option 'A' - "It gets extinguished" - is the correct answer.

A burning substance will be extiniguished if the temperature fall below its ignition temperature