The solution scatters a beam of light passing through it.
Explanation
A true solution is a homogeneous mixture of two or more substances where the solute is completely dissolved in the solvent. The properties of a true solution are defined by the extremely small size of its constituent particles.
Analysis of Options:
- The particles are smaller than 1 nm in diameter. is a property of true solutions: The particles in a true solution are smaller than 1 nm ($10^{-9}$ m) in diameter. This extremely small size prevents them from being seen by the naked eye.
- The solution scatters a beam of light passing through it. is NOT a property of true solutions: True solutions do not scatter a beam of light passing through them. The scattering of light, known as the Tyndall effect, is a characteristic of colloids and suspensions where particles are large enough to interact with light rays. In true solutions, the path of light is not visible.
- The mixture is homogeneous in nature. is a property of true solutions: A true solution is homogeneous in nature, meaning the composition and properties are uniform throughout the mixture.
- The solute particles cannot be separated by filtration. is a property of true solutions: Due to their microscopic size (molecular or ionic level), solute particles pass easily through filter paper. Therefore, the components cannot be separated by simple filtration.
Key Takeaway:
True solutions are characterized by particle sizes less than 1 nm, a homogeneous nature, and the inability to scatter light (absence of the Tyndall effect). The Tyndall effect is observed in colloids, not true solutions.