The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light

Options

A. is scattered the most by smoke or fog
B. is scattered the least by smoke or fog
C. is absorbed the most by smoke or fog
D. moves fastest in air

Explanation

To solve the question regarding why red danger signals on tall buildings can be easily seen from a distance, we can analyze the properties of light and how different colors behave in the atmosphere, particularly in the presence of smoke or fog.

### Step-by-Step Solution:

1. **Understanding Light Scattering**:
- Light scattering occurs when light rays encounter particles in the atmosphere, such as smoke or fog. Different colors of light scatter differently based on their wavelengths.

2. **Wavelength of Colors**:
- The visible spectrum of light includes various colors, each with a different wavelength. Red light has a longer wavelength compared to other colors like blue or green.

3. **Rayleigh Scattering**:
- Rayleigh scattering explains that shorter wavelengths (like blue and violet) scatter more than longer wavelengths (like red). This means that red light is less affected by scattering in the presence of particles.

4. **Conclusion from Scattering Behavior**:
- Since red light has the longest wavelength, it is scattered the least by smoke or fog. This property allows red signals to remain visible even in poor visibility conditions.

5. **Choosing the Correct Option**:
- Given the options:
- Option 1: Red light is scattered the most by smoke or fog.
- Option 2: Red light is scattered the least by smoke or fog.
- Option 3: Red light is absorbed the most by smoke or fog.
- Option 4: Red light moves fastest in air.
- The correct answer is **Option 2**, as red light is indeed scattered the least by smoke or fog.

### Final Answer:
The danger signals installed at the top of tall buildings are red in color because the red light is scattered the least by smoke or fog.

---