Correct Answer: Sales tax

Solution : The correct answer is (d) Sales tax

Sales tax is not included in the calculation of national income. National income measures the total value of goods and services produced within a country's borders over a specific period. Rental income, interest income, and capital gains are components of national income as they represent income earned by individuals or businesses within the country. Sales tax, on the other hand, is a tax imposed on the sale of goods and services and is not considered as part of national income because it represents a transfer of funds from consumers to the government rather than income generated from productive activities.