At the minimum point of the long run average cost curve .......... is observed.

Option 1 -> Decreasing Returns to Scale occurs when the LRAC is rising, after the minimum point.

Option 2 -> Constant Returns to Scale occurs at the minimum point of LRAC where output increases proportionately with inputs.

Option 3 -> Law of Variable Proportions applies to short run with fixed inputs, not relevant to LRAC minimum.

Option 4 -> Increasing Returns to Scale occurs when LRAC is falling, before reaching the minimum point.

---

Hence, Constant Returns to Scale -> At the minimum point of the long run average cost curve, the firm achieves its optimal scale of production. Here, a proportionate increase in all inputs leads to an exactly proportionate increase in output. The average cost is neither increasing nor decreasing, indicating the most efficient scale of operation where constant returns to scale are observed. This is the transition point between economies of scale (increasing returns) and diseconomies of scale (decreasing returns). -> correct