Final answer:
The SRAS curve is initially horizontal in the Keynesian model because it represents a recessionary economy with high unemployment. Changes in aggregate demand primarily affect output and employment, not prices.
Step-by-step explanation:
In the Keynesian model, the SRAS curve is initially horizontal in the Keynesian zone because it represents a situation of high unemployment and a recessionary gap. In this zone, the equilibrium level of real GDP is far below potential GDP, indicating a recessionary economy with high cyclical unemployment.
The horizontal SRAS curve means that changes in aggregate demand (AD) will primarily affect output and employment but have little impact on prices.