Something that isn't consumed by the reaction (so say A) is dissolved at the same time as something that is consumed by the reaction (B) in a solvent, so that they are in the same phase...what is this reaction an example of?
What is the most pervasive particle that is involved in an example of this type of reaction that isn't consumed by the reaction?
catalyst?
perhaps even 'homogeneous catalyst'.
But the question does not state the the material takes part in the reaction, it just 'isn't consumed', so it could be a non-reacting impurity, so that the reaction is a one phase homogeneous reaction where A is a non-reacting imputity.
Based on the information you provided, it appears that you are describing a reaction in which two substances, A and B, are dissolved in a solvent and are in the same phase. Substance A is not consumed by the reaction, while substance B is consumed.
This type of reaction you are describing is an example of a heterogeneous reaction. In a heterogeneous reaction, the reactants exist in different phases. However, in your case, since both substances A and B are in the same phase (dissolved in the solvent), it could also be considered a homogenous reaction.
Now, to answer your second question, the most pervasive particle involved in this type of reaction that is not consumed by the reaction would be substance A. Since substance A is not consumed, it remains in the reaction mixture and is not depleted during the reaction. Therefore, it is the most pervasive particle that is present throughout the reaction.