The correct answer is B. 98 per cent.
A power transformer is a device that transfers electrical energy from one circuit to another without changing the frequency. It does this by using electromagnetic induction to create a magnetic field that induces a voltage in a second coil. The efficiency of a power transformer is the ratio of the output power to the input power. It is typically expressed as a percentage.
The efficiency of a power transformer is affected by a number of factors, including the design of the transformer, the quality of the materials used, and the operating conditions. The efficiency of a power transformer is typically around 98%. This means that for every 100 watts of input power, the transformer will produce 98 watts of output power.
The efficiency of a power transformer is important because it can affect the overall cost of electricity. A transformer that is less efficient will use more power, which will result in higher electricity bills.
Option A is incorrect because the efficiency of a power transformer is not 100%. There are always some losses in the transformer, such as heat loss.
Option C is incorrect because the efficiency of a power transformer is typically around 98%.
Option D is incorrect because the efficiency of a power transformer is typically around 98%.