The mixture is a colloid because two different substances can be seen in a small sample when observed under a microscope.
Option D
Explanation:
Colloid is a heterogeneous mixture of two or more substances with relatively smaller size of solute particles and thus it appears to be a homogeneous mixture.
Particles present in a colloidal solution cannot be differentiated through naked eye observations and hence when Maria examined the sample under a microscope, two different substances were seen. Maria saw the mixture to be same throughout since the solute particles were very small in size and evenly dispersed in the solvent.
