Question

why a solution is always clear and transparent

Answer 1

It is so because, a true solutions is a homogeneous mixture.That is, the solute and the solvent cannot be distinguished even under a microscope.
The particles are in the size of 10⁻¹⁰. And they do not scatter light.
That is why, a solution is always clear and transparent.

Answer 2

This is not compulsory that a solution is always clear and transparent.We can say that a true solution is always clear and transparent.The particles are in the size of 10⁻¹⁰.