The ratio of increase in income to increase in investment is termed as

Option 1 -> Marginal propensity to save is the ratio of change in savings to change in income (ΔS/ΔY).

Option 2 -> Marginal propensity to consume is the ratio of change in consumption to change in income (ΔC/ΔY).

Option 3 -> Marginal propensity to invest is the ratio of change in investment to change in income (ΔI/ΔY).

Option 4 -> Investment Multiplier is the ratio of change in income to change in investment (ΔY/ΔI).

Hence, Investment Multiplier -> The investment multiplier (k) measures the ratio of increase in national income (ΔY) to the increase in investment (ΔI). The formula is k = ΔY/ΔI or k = 1/(1-MPC) or k = 1/MPS. It shows the amplified effect that an initial change in investment has on total income through rounds of spending in the economy. For example, if the multiplier is 4, then a $100 increase in investment leads to a$400 increase in national income -> correct