Amixture has particles that cannot be seen but do reflect light. should be classified as a (homogeneous mixture, suspension, solution, colloid)

The answer you are looking for would be Colloid, because in colloid mixtures, the particles are big enough to reflect them in a way. Colloids can be distinguished from solutions using the Tyndall effect. Light passing through a colloidal dispersion, such as smoke or foggy air, will be reflected by the larger particles and the light beam will be visible. 

Exothermic,  physical change after it is already baked

Nonmetals usually react by gaining electrons