The function of the investment multiplier is?

$ΔY/ Δ\bar Α$

The correct answer is Option (4) → $ΔY/ Δ\bar Α$

The ratio of the total increment in equilibrium value of final goods output to the initial increment in autonomous expenditure is called the investment multiplier of the economy.

The investment multiplier = $ΔY/ Δ\bar Α$

                                       = 1 / (1- c) = 1 / S

where ΔY is the total increment in final goods output and c = mpc.  

The size of the multiplier depends on the value of c multiplier increases.

Note: Note: The given answer is as per NTA and NCERT, i.e., Option (4). However, Option (3) can also be considered correct because the investment multiplier specifically measures how much total income changes in response to a change in investment. Therefore, it can be expressed as the ratio of change in income to change in investment, making Option (3) conceptually valid as well.