Which type of function must be used to access a picklist field in a formula?

To access a picklist field in a formula within Salesforce, the correct approach involves the use of the ISPICKVAL function. This function is specifically designed for evaluating whether a picklist field has a certain value. It checks the value of a picklist field against a specified string and returns true if there is a match. Utilizing ISPICKVAL ensures that you are correctly handling the specific nature of picklist fields, as they can contain multiple predefined values.

The other options, while useful in different contexts, do not serve the purpose of directly evaluating picklist values. The Date Today() function is focused on returning the current date, making it irrelevant for accessing picklist fields. The Case function is typically employed for evaluating a range of conditions, but again, it does not specifically facilitate the access to or comparison of picklist field values. Similarly, the IF/Then statements can perform various logic operations but lack the specialized capability to deal with picklist fields efficiently. Therefore, the ISPICKVAL function is the designated method for handling comparisons with picklist fields in formulas.