Which of the following is considered an extraordinary item on the income statement?

Extraordinary items on the income statement are defined as gains or losses that are both unusual in nature and infrequent in occurrence. These items are typically not part of the regular operations of a business and should stand out due to their unique characteristics.

In the context of the provided options, insurance proceeds from natural disasters fall within the realm of extraordinary items. Such proceeds are usually infrequent because natural disasters occur sporadically, and they are considered unusual because the average business does not regularly engage in activities involving disasters that lead to insurance claims. Therefore, recording these proceeds as an extraordinary item helps to provide users of the financial statements with a clearer picture of the company's ongoing performance by separating these unusual events from regular business income.

The other options do not meet the criteria for extraordinary items. Regular business revenue and operating income are typical results of a company's core operations, while gains from the sale of assets, while they can be infrequent, generally do not carry the same level of unusual nature as proceeds from natural disasters. Thus, they do not qualify as extraordinary items under accounting standards.