Solution
Option 1 -> In equilibrium, aggregate demand equals aggregate supply, determining the output level which directly influences employment.
Option 2 -> Factors of production are inputs used in production but don't determine employment levels independently.
Option 3 -> Capital is one factor of production but alone doesn't determine overall employment in the economy.
Option 4 -> Raw materials are necessary for production but are not the primary determinant of employment levels.
Hence, Output Equilibrium -> According to Keynesian economics, the level of employment in an economy is determined by the equilibrium level of output (where aggregate demand equals aggregate supply). When output is at equilibrium, it determines how much production is needed, which in turn determines how much labor (employment) is required. The economy's employment level adjusts based on the output that firms need to produce to meet aggregate demand. This is why output equilibrium is the key determinant of employment levels in an economy. -> correct