The correct answer is option 'D' - 1200 - 2500°C.

Radiation pyrometers are instruments used for measuring high temperatures based on the principle of thermal radiation. They are commonly used in industrial applications where non-contact temperature measurements are required.

Let's understand why the correct answer is option 'D' in detail:

1. Introduction to Radiation Pyrometers:
- Radiation pyrometers work on the principle of measuring the intensity of thermal radiation emitted by a hot object.
- The amount of radiation emitted by an object is directly related to its temperature.
- By measuring the intensity of this radiation, the temperature of the object can be determined.

2. Temperature Range of Radiation Pyrometers:
- Different types of radiation pyrometers are designed for different temperature ranges.
- The temperature range of a radiation pyrometer depends on the type of sensor and its design.
- Option 'D' - 1200 - 2500°C is the correct answer because it represents the temperature range where radiation pyrometers are typically used.

3. Explanation of the Temperature Range:
- Radiation pyrometers are commonly used for high-temperature measurements, especially in industrial processes.
- Option 'A' - 0 - 500°C represents a lower temperature range. There are other types of temperature sensors, like thermocouples and resistance thermometers, which are more suitable for this range.
- Option 'B' - 500 - 1000°C is also a lower temperature range. Radiation pyrometers can be used within this range, but they are more commonly used for higher temperatures.
- Option 'C' - (-250) - 500°C represents a wide temperature range, including negative temperatures. However, radiation pyrometers are not typically used for negative temperatures.
- Option 'D' - 1200 - 2500°C represents a higher temperature range. This range is commonly encountered in industrial processes such as metal smelting, glass manufacturing, and high-temperature furnaces. Radiation pyrometers are often used for temperature measurements in these applications.

In conclusion, option 'D' - 1200 - 2500°C is the correct answer because it represents the temperature range where radiation pyrometers are commonly used. These instruments are designed to measure high temperatures, making them suitable for industrial applications requiring non-contact temperature measurements.