What metric is national output measured by?

National output is primarily measured by Gross Domestic Product (GDP). GDP represents the total monetary value of all finished goods and services produced within a country's borders in a specific time period. It serves as a comprehensive measure of a nation's overall economic activity, reflecting the health, size, and growth of its economy.

GDP provides insights into how well an economy is performing and is often used to compare economic activity between different countries or periods. It takes into account various sectors, including consumer spending, government expenditure, business investments, and net exports (exports minus imports), capturing the overall economic performance rather than just profits or financial market performance.

The metrics associated with the other choices do not directly measure national output in the same broad sense. For instance, while net profit pertains specifically to a company's financial performance, market capitalization relates to the total value of a company's shares and trade balance focuses on the difference between a country's exports and imports. Therefore, GDP is the most relevant metric for assessing a nation’s overall economic output.