Which of the following is not part of prime cost of production?

Depreciation of factory equipment is not part of prime cost of production. Prime cost refers to the total cost of direct materials, direct wages, and direct expenses incurred in the production of a product. Depreciation is a non-cash expense and does not represent any actual expenditure of cash in the production process. Instead, it represents the wear and tear on the factory equipment over time. Therefore, it is not included in the calculation of prime cost.