Which form of active ingredient is also required for prescription labeling if applicable?

The active ingredient that must be included on prescription labeling, when applicable, is the net quantity. This information is crucial because it informs patients and healthcare providers of the exact amount of the active ingredient contained within the prescription. Including the net quantity on the label helps to ensure proper dosing and minimizes the risk of dosage errors. It is an essential aspect of prescription labeling standards and contributes to safe medication practices.

While other options like amended descriptions, preserved ratios, and dosage forms are important in the context of pharmaceuticals, they do not specifically address the requirement for labeling as it pertains to the net quantity of the active ingredient. Therefore, net quantity stands out as the necessary element mandated by prescription labeling regulations.