ANS:C - product enrichment.

Refluxing of part of the distillate in a fractionating column is primarily aimed at product enrichment. When reflux occurs, some of the condensed vapor is returned back to the column. This helps in increasing the contact between the rising vapor and the descending liquid. As a result, it allows for better separation of components, leading to higher purity of the desired product. Therefore, refluxing is primarily aimed at product enrichment. While it does aid in heat conservation to some extent by returning condensed vapors, and it can indirectly enhance yield by improving separation efficiency, its primary purpose is to enrich the product. So, the correct answer is: Product enrichment.