Option 1 -> Autonomous investment refers to investment that is independent of income levels, not a ratio.
Option 2 -> Investment multiplier measures the ratio of change in equilibrium output to initial change in autonomous expenditure.
Option 3 -> Ex-ante investment is planned investment before actual occurrence, not a ratio concept.
Option 4 -> GDP multiplier is not the standard term; the correct term is investment multiplier.
Hence, Investment multiplier -> The investment multiplier (or Keynesian multiplier) captures the amplified effect of autonomous expenditure changes on total output. When autonomous spending increases by ₹1, the total output increases by more than ₹1 due to the circular flow of income. For example, if the multiplier is 4, a ₹100 increase in autonomous investment leads to a ₹400 increase in equilibrium GDP. The formula is k = 1/(1-MPC) or 1/MPS, where MPC is marginal propensity to consume and MPS is marginal propensity to save. -> correct