Final answer:
In a manufacturing firm, period costs include all non-manufacturing costs such as sales, marketing, and administrative expenses that are not directly involved in the production process.
Step-by-step explanation:
In a manufacturing firm, period costs are the costs that are not directly tied to the production process and therefore are expensed in the period in which they are incurred, rather than being capitalized into the cost of goods sold. Period costs include all non-manufacturing costs, which can encompass sales and marketing expenses, general and administrative expenses, and other costs that cannot be directly connected to the creation of a product. These costs are contrasted with product costs, which include direct materials, direct labor, and manufacturing overhead and are capitalized as part of the inventory value until the goods are sold. So, in the context of the options provided, period costs include all non-manufacturing costs (option 5).