Question

if any solution is given how will i identify that it is colloidal or not ?d size of the particles should be big what else?

Answer 1

Colloidal particles scatter light
if you will pass a beam of light through a colloid solution, colloidal particles will scatter light and you will be able to see the path of the light.

In case of true solution (e.g., salt in water) there is so little scattering of the light that the path of the light cannot be seen. 

So, you can identify whether the solution is colloidal or not by passing light through it.

Answer 2

The solutions in which the particles easily scatter a beam of visible light are colloidal solutions. We can say a solution is colloidal if it can scatter a beam of light whose path should be visible.The particles should be very minute in the size of 1nanometers to 100nanometers. By following this we can identify a solution as colloidal or not. Hope this helps you