When an economy is operating under conditions of full employment, the production of more of commodity A will mean the production of less of commodity B because

When an economy is operating under conditions of full employment, the production of more of commodity A will mean the production of less of commodity B because "resources are limited".

Explanation:

The optimal employment rate in an economy, where there is no involuntary unemployment between workers. Full employment of workers is one element of an economy that operates at its maximum productive potential and produces at a time along the frontier of its production capabilities. The Federal Reserve sees a baseline unemployment rate of 5.0 to 5.2 per cent as the economy's "full employment". Resources are always limited thus if one portion is increasing another will surely decrease.