In meeting federal specifications, insulated units must have the following fire-resistant minimum ratings:

The correct answer is associated with Class 350's one-hour fire-resistance rating, which is stipulated in federal specifications for insulated units. This rating indicates that the material or assembly can withstand fire exposure for a minimum of one hour without losing its structural integrity or containment of fire.

Class 350 ratings are often relevant in protecting buildings and occupants from the spread of fire, especially in life safety and property protection scenarios. A one-hour rating is significant because it allows for enough time to either control the fire, evacuate occupants, or both, thereby minimizing risk and ensuring safety protocols are adhered to.

In contrast, higher ratings such as those proposed in other answer choices would exceed the requirements outlined for the specific class unit in question and potentially lead to unnecessary cost or material specifications not aligned with federal guidelines for the intended applications. Therefore, understanding these classifications helps ensure compliance with fire safety regulations while effectively managing resources.