The Correct Answer: The correct answer is 'will turn off'.

Explanation:

When we see the phrase "if its idle for half an hour," it indicates a condition that will trigger the action of turning off. In this case, the condition is the idle state of the subject, which is not specified in the sentence. However, based on the context, we can assume that the subject refers to a device or an appliance that has an automatic shutdown feature.

Future Simple Tense: The future simple tense is used to describe actions that will happen in the future. It is formed by using the auxiliary verb "will" followed by the base form of the main verb. In this case, the main verb is "turn off," and when combined with "will," it forms the future simple tense "will turn off."

Automatic Shutdown: The sentence states that the subject will turn off automatically. This implies that the device or appliance has a built-in mechanism that detects inactivity and initiates the shutdown process. The purpose of this feature is usually to conserve energy or prevent unnecessary usage.

Idle for Half an Hour: The condition for the automatic shutdown is being idle for half an hour. This means that if the subject remains inactive or unused for a continuous period of thirty minutes, it will trigger the automatic shutdown.

Assumptions: Although the sentence does not provide specific information about the subject, we can assume that it refers to a device or appliance that has an automatic shutdown feature. Examples of such devices could be a computer, television, or any other electronic device that is designed to conserve energy by turning off when not in use.

Overall, the correct answer is "will turn off" because it accurately represents the future action of the subject, which is an automatic shutdown triggered by a period of inactivity.