The correct answer is: A. no losses and magnetic leakage.
An ideal transformer is a theoretical device that has no losses and no magnetic leakage. This means that all of the input power is transferred to the output, and there is no loss of energy due to resistance or other factors. The ideal transformer also has a perfect magnetic core, which means that all of the magnetic flux generated by the primary winding is coupled to the secondary winding. This results in a perfect transfer of power from the primary to the secondary winding.
In practice, no transformer is truly ideal. There will always be some losses due to resistance and other factors. However, ideal transformers are a useful theoretical model that can be used to understand the operation of real transformers.
Option B, interleaved primary and secondary windings, is not a characteristic of an ideal transformer. In fact, interleaved windings can actually increase losses in a transformer.
Option C, a common core for its primary and secondary windings, is a characteristic of many transformers, but it is not a requirement for an ideal transformer.
Option D, core of stainless steel and winding of pure copper metal, is a common choice of materials for transformers, but it is not a requirement for an ideal transformer.
In conclusion, the correct answer is: A. no losses and magnetic leakage.