The correct answer is: D. Infinity
A transformer is an electrical device that transfers energy between two or more circuits through electromagnetic induction. It does this by using two coils of wire that are wrapped around a common core. The primary coil is connected to the input voltage, and the secondary coil is connected to the load. When current flows through the primary coil, it creates a magnetic field. This magnetic field then induces a voltage in the secondary coil. The voltage in the secondary coil is proportional to the number of turns in the secondary coil and the ratio of the number of turns in the primary coil to the number of turns in the secondary coil.
The resistance between the primary and secondary coils of a transformer should be infinity. This is because the primary and secondary coils are not connected electrically. The only connection between the two coils is the magnetic field that is created by the current flowing through the primary coil. The magnetic field is what induces the voltage in the secondary coil.
If there were any resistance between the primary and secondary coils, it would cause a voltage drop. This voltage drop would reduce the amount of voltage that is available to the load. In addition, the resistance would cause heat to be generated. This heat would cause the transformer to become hot, which could damage the transformer.
Therefore, the resistance between the primary and secondary coils of a transformer should be infinity.