Final answer:
Among the given options, 'Interest income' (1) is NOT an expense; it is a type of revenue, whereas the other options listed represent expenses.
Step-by-step explanation:
The question asks which of the following is NOT an expense. Expenses are costs incurred in the process of earning revenue. In this list, options 2) Salaries paid to beauticians, 3) Real estate taxes paid on personal residence, and 4) Contributions to charity are all expenses. However, 1) Interest income is not an expense; it is a type of revenue. Expenses would include the costs of recreation (such as televisions, pets and pet products, sports equipment), costs of education and communication (like college tuition and telephone services), and more specific costs like those for apparel or transportation.