D. High permeability

The properties that are desirable in the material for the transformer core are:

A. Mechanical strength: The core material should be able to withstand the mechanical stresses caused by the transformer’s operation without deforming or breaking.

B. Low hysteresis loss: Hysteresis loss occurs when the core material’s magnetization lags behind the applied magnetic field. Low hysteresis loss means that the core material requires less energy to maintain a magnetic field, which results in less heat being generated and less energy being wasted.

C. High thermal conductivity: The core material should be able to dissipate heat effectively, to prevent overheating and damage to the transformer.

D. High permeability: High permeability means that the core material is a good conductor of magnetic fields. This is not necessarily desirable because it will lead to a large core and more energy loss.