Final answer:
Block 11c of the CMS-1500 form is used to indicate secondary insurance coverage and the name of the commercial health insurance plan.
Step-by-step explanation:
Block 11c of the CMS-1500 form is used to indicate secondary insurance coverage. This means that if the patient has multiple insurance plans, the information about the secondary insurance plan should be entered in this block. The name of the commercial health insurance plan should be provided here, along with any relevant policy information.