Which one of the following statements is not correct ?

Options

A. Tyndall effect in colloidal solution solution is due to scattering of light
B. Hardy - Schuize rule is applicable only to the coagulation of lyophilic sols
C. Bule colour of the sky is due to scattering of light by dust particies
D. Greater flocculation value on an electrolyte means its poor coagulating power

Answer

To determine which statement is not correct, let's analyze each statement provided in the question:

1. **Tyndall effect in colloidal solution is due to scattering of light.**
- This statement is correct. The Tyndall effect occurs when light is scattered by colloidal particles, making the path of the light visible.

2. **The Hardy-Soulier rule is applicable only to the coagulation of lyophilic sols.**
- This statement is **not correct**. The Hardy-Soulier rule applies to both lyophilic and lyophobic sols. It explains how the presence of electrolytes can cause coagulation by neutralizing the charges on the particles.

3. **The blue color of the sky is due to scattering of light by dust particles.**
- This statement is correct. The blue color of the sky is primarily due to Rayleigh scattering of sunlight by the molecules and small particles in the atmosphere.

4. **Greater the flow coagulation value, poorer the coagulating power.**
- This statement is correct. A higher flow coagulation value indicates that more electrolyte is needed to cause coagulation, which means the coagulating power is weaker.

### Conclusion:
The statement that is **not correct** is: **The Hardy-Soulier rule is applicable only to the coagulation of lyophilic sols.**