For a good transformer, the material of the core should have the hysteresis loop of:

Explanation

The explanation is: The core of the transformer should be assembled from the laminated sheets of a material whose hysteresis loop area is very small. This is because a small hysteresis loop area indicates lower hysteresis losses in the core material. Hysteresis losses occur due to the repeated magnetization and demagnetization cycles of the core material as the alternating current passes through the transformer. The energy dissipated as heat during these cycles leads to inefficiencies in the transformer. By minimizing hysteresis losses through the use of a core material with a small hysteresis loop area, the transformer can operate more efficiently, leading to reduced energy wastage and improved overall performance.