According to which theory, the equilibrium level of income is determined where planned level of aggregate demand is equal to planned level of aggregate supply?

Keynesian theory

The correct answer is Option 3: Keynesian theory

According to Keynesian theory, the equilibrium level of income is determined where planned level of aggregate demand is equal to planned level of aggregate supply. Income/output/employment are in equilibrium at that level where the AD = AS i.e. aggregate demand is equal to aggregate supply.