Introduction:
In this question, we are asked to determine the condition under which the average current rating of a semiconductor diode will be maximum. The options given are half-wave rectified AC, full-wave rectified AC, pure DC, and pure AC. The correct answer is option C, pure DC. Let's understand why.

Explanation:
A semiconductor diode is a two-terminal electronic component that allows current to flow in only one direction and blocks it in the opposite direction. It conducts when forward-biased and blocks when reverse-biased.

Half-wave rectified AC:
- In half-wave rectified AC, only one-half cycle of the input AC waveform is allowed to pass through the diode.
- The diode conducts during the positive half-cycle and blocks during the negative half-cycle.
- As a result, the average current is lower compared to other options.

Full-wave rectified AC:
- In full-wave rectified AC, both halves of the input AC waveform are allowed to pass through the diode.
- The diode conducts during both the positive and negative half-cycles.
- Although the average current is higher compared to half-wave rectified AC, it is still not the maximum.

Pure AC:
- Pure AC refers to an alternating current in which the direction of current flow continuously changes.
- In this case, the diode will conduct and block alternatively with each half-cycle.
- Since the diode blocks current flow in one-half cycle, the average current is lower compared to pure DC.

Pure DC:
- Pure DC refers to a direct current in which the direction of current flow remains constant.
- In this case, the diode remains forward-biased throughout, allowing current to flow continuously in one direction.
- As a result, the average current rating of the diode will be maximum under pure DC conditions.

Conclusion:
The average current rating of a semiconductor diode will be maximum for pure DC conditions. Under pure AC conditions, the diode blocks current flow in one-half cycle, resulting in a lower average current.