The INCORRECT statements below regarding colloidal solutions is:

Let us examine each statement about colloidal solutions:

Option (1): A colloidal solution shows colligative properties. This is correct. Colloidal solutions, like true solutions, exhibit colligative properties such as osmotic pressure, though the effects are much smaller due to the large size of colloidal particles (and hence fewer particles per unit mass).

Option (2): An ordinary filter paper can stop the flow of colloidal particles. This is incorrect. Colloidal particles (size range 1-1000 nm) are small enough to pass through ordinary filter paper, which has pore sizes much larger than colloidal particles. Only ultra-filters (with very fine pores) or semipermeable membranes can separate colloidal particles. This is one of the key differences between colloidal solutions and suspensions.

Option (3): The flocculation power of $$Al^{3+}$$ is more than that of $$Na^+$$. This is correct. According to the Hardy-Schulze rule, the coagulating power of an ion increases with its charge. Since $$Al^{3+}$$ has a higher charge than $$Na^+$$, it has a greater flocculation (coagulation) power.

Option (4): A colloidal solution shows Brownian motion of colloidal particles. This is correct. Colloidal particles exhibit Brownian motion due to continuous bombardment by molecules of the dispersion medium.

The incorrect statement is option (2).