The correct answer is D. Insurance charges.
Fixed costs are costs that do not change with the level of production. They are typically incurred regardless of whether the plant is operating or not. Examples of fixed costs include depreciation, property taxes, and insurance charges.
Fuel cost is a variable cost, which means that it changes with the level of production. The more electricity that is produced, the more fuel will be required. Interest on capital is also a variable cost, as it is based on the amount of money that has been borrowed to finance the plant. Depreciation is a non-cash expense that is used to account for the wear and tear on the plant’s assets. Property taxes are a fixed cost that is based on the value of the plant’s assets.
In conclusion, the only option that is not a fixed cost is D. Insurance charges.