The lowest temperature at which the substance starts burning is called_______.
A. Minimum temperature
B. Maximum temperature
C. Boiling temperature
D. Ignition temperature

Hint: For a fire to exist there is a need for three things namely fuel, oxygen, and heat. If all these conditions are fulfilled then there can be the existence of fire. When all the necessary conditions are met then the temperature at which the fire just starts to form is the lowest temperature that is needed for the fuel to start burning. Any temperature below this lowest temperature will be unable for the burning process to take place. Any temperature above the lowest temperature will favor the burning process as long as the other conditions are fulfilled.

Complete step by step answer:
Three things are essential for the fire to be produced namely fuel, oxygen, and required temperature. If anyone of the conditions is not satisfied the fire will not start.
We place the fuel in the presence of oxygen and provide heat. Upon achieving the required temperature the fuels start to burn by catching fire. This temperature where the fuels start burning is called the ignition temperature or the kindling temperature.
The burning fuel produces a flame that depends on the amount of oxygen present .the burning fuel produces a mixture of carbon compounds like carbon dioxide, carbon monoxide, etc.
Generally, the flame produced is either blue or yellow. The blue flame also called the non-luminous flame is produced when the fuel burns completely in the presence of an excess of oxygen.it has ha very high temperature
The yellow flame also called the luminous flame is produced in an environment where there is not enough oxygen present. The unburnt parts of the fuels glow in the flame producing the luminous flame. Its temperature is less than that of the blue or non-luminous flame.

So, the correct answer is Option D.

Note: 1. Fires that burn at a temperature like $400^\circ C$ are called cool flames.
2. Burning and catching fire are two different things. Paper may start burning or discoloration at the temperature of $150^\circ C$ but catches fire at nearly $230^\circ C$.
3. The flashpoint is the temperature at which the fuel oil gives vapors which form flashes when exposed to flame.
4. The fire point is the temperature at which the oil must be heated for it to continue to burn when exposed to an open flame