The lowest temperature at which substance catch fire is called ignition temperature.....so the correct answer is D.

The correct answer is option 'D' - ignition temperature.

Explanation:
The ignition temperature is the lowest temperature at which a substrate or material catches fire and starts to burn. It is also known as the kindling temperature or autoignition temperature. This temperature varies for different substances and is an important factor in understanding fire safety and prevention.

**Factors Affecting Ignition Temperature:**

Several factors influence the ignition temperature of a substance. Some of these factors include:

1. **Chemical composition:** Different substances have different ignition temperatures. For example, some flammable liquids may have lower ignition temperatures compared to solid materials. Substances with higher chemical reactivity tend to have lower ignition temperatures.

2. **Surface area:** The surface area of a material can affect its ignition temperature. Finely divided materials, such as powders or dust, have a larger surface area and can ignite more easily than solid blocks of the same material.

3. **Presence of contaminants:** The presence of contaminants or impurities can lower the ignition temperature of a substance. These contaminants can act as catalysts or provide additional fuel for the fire.

4. **Oxygen concentration:** Oxygen is necessary for combustion to occur. The availability of oxygen can affect the ignition temperature. Higher oxygen concentrations can lower the ignition temperature, making it easier for a substance to catch fire.

**Importance of Ignition Temperature:**

Understanding the ignition temperature of a substance is crucial for fire safety and prevention. It helps in:

1. **Fire prevention:** Knowing the ignition temperature of materials allows us to take precautions to prevent fires. By keeping flammable substances away from potential ignition sources and controlling factors like temperature and oxygen concentration, we can reduce the risk of fires.

2. **Fire suppression:** Firefighters and fire safety professionals use knowledge of ignition temperatures to extinguish fires effectively. By using firefighting techniques such as cooling, removing fuel sources, or reducing oxygen supply, they can prevent the fire from spreading and extinguish it.

3. **Material selection:** Ignition temperature is an important consideration in material selection for various applications. Industries that deal with flammable materials need to choose materials with higher ignition temperatures to minimize the risk of fire accidents.

In conclusion, the ignition temperature is the lowest temperature at which a substrate catches fire. Understanding the ignition temperature of different substances helps in fire prevention, suppression, and material selection for various applications.