Which one of the following statements is not true about thermal radiations ?.

Options

A. All bodies emit thermal radiations at all temperature
B. Thermal radiations are electromagnetic waves
C. Thermal radiations are not reflected from a mirror
D. Thermal radiations travel in free space with a velocity of `3xx 10^(8)ms^(-1)`

Explanation

To determine which statement is not true about thermal radiations, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: All bodies emit thermal radiation at all temperatures.**
- This statement is true. According to the laws of thermodynamics, any body with a temperature above absolute zero (0 Kelvin) emits thermal radiation. The amount of radiation emitted increases with temperature.

2. **Statement 2: Thermal radiations are electromagnetic waves.**
- This statement is also true. Thermal radiation is indeed a form of electromagnetic radiation, which can include infrared radiation, visible light, and ultraviolet radiation, depending on the temperature of the emitting body.

3. **Statement 3: Thermal radiation are not reflected from a mirror.**
- This statement is false. Thermal radiation, being electromagnetic waves, can be reflected by mirrors. Just like visible light, thermal radiation can be reflected off surfaces that are smooth and shiny, such as mirrors.

4. **Statement 4: Thermal radiations travel in free space with a velocity of \(3 \times 10^8\) m/s.**
- This statement is true. The speed of electromagnetic waves, including thermal radiation, in a vacuum (free space) is approximately \(3 \times 10^8\) m/s, which is the speed of light.

### Conclusion:
The statement that is not true about thermal radiation is **Statement 3: Thermal radiation are not reflected from a mirror.**