9.  An entry that results in a debit to an expense account and a credit to a related liability account is an example of which category of adjusting entries?

The entry you're referring to is an example of an Accrued Expense.

Here's the step-by-step explanation:

1. Accrued expenses are expenses that have been incurred but not yet paid.

2. When an expense is recognized before it is paid, a liability is created. This liability represents the amount owed for the expense.

3. The adjusting entry to record an accrued expense involves a debit to an expense account, which increases the total expense, and a credit to a liability account, which increases the total liabilities.

4. This type of adjusting entry ensures that expenses are recognized in the period they are incurred rather than in the period they are paid. This is in accordance with the accrual basis of accounting, which records revenues and expenses when they are earned or incurred, regardless of when cash is exchanged.

So, the category of adjusting entries that this falls under is "Accrued Expenses".