Select correct statement/s regarding colloids:Colloidal particles of Au and Ag are negatively chargedColloidal particles of methylene blue dye are positively chargedGelatin can be protective colloid to prevent flocculation of hydrated metal oxides solsCongo red dye can be protective colloid to prevent flocculation of CdS sols

All the statements are correct:

1. Colloidal particles of Au and Ag are negatively charged: This is true. Gold and silver colloids are usually prepared by reducing their salts in the presence of a protective colloid. The resulting particles carry a negative charge due to the adsorption of anions from the solution.

2. Colloidal particles of methylene blue dye are positively charged: This is also true. Methylene blue dye forms a positively charged colloid because it is a cationic dye. The positive charge is due to the presence of extra protons on the nitrogen atoms in the dye molecule.

3. Gelatin can be a protective colloid to prevent flocculation of hydrated metal oxides sols: This is correct. Gelatin, being a protein, can adsorb onto the surface of the colloidal particles and prevent them from coming together and flocculating. This is because the gelatin molecules form a protective layer around the particles, keeping them apart.

4. Congo red dye can be a protective colloid to prevent flocculation of CdS sols: This is also correct. Congo red dye can adsorb onto the surface of the CdS particles and prevent them from flocculating. This is because the dye molecules form a protective layer around the particles, keeping them apart.