Correct Answer: Gross Domestic Product (GDP)

Solution : The correct answer is (a) Gross Domestic Product (GDP)

Gross Domestic Product (GDP) is the most commonly used measure to represent national income. It quantifies the total market value of all final goods and services produced within a country's borders during a specific time period, typically a year. GDP includes the income earned by all factors of production, including labor, capital, and land, in the production process.

In summary, while national income is a broader concept, Gross Domestic Product (GDP) is the specific term used to measure national income and represents the market value of all final goods and services produced within a country's borders.