According to Nyaya (Classical Indian School of logic) the fallacy of irregular middle is called:

The correct option is Anaikantika.

In classical Indian logic (Nyaya), fallacies of inference are known as Hetvabhasa (literally, "looks like a reason but is not"). A valid inference relies on a middle term (hetu) that is invariably associated with the major term (sadhya). When this relationship is violated, a fallacy arises.

The fallacy of the irregular middle term is called Anaikantika (also known as Savyabhichara). This occurs when the middle term is not uniformly or exclusively related to the major term, leading to more than one possible conclusion. Because the middle term is irregular and wanders beyond the class of the major term, it fails to establish a certain and singular conclusion.

To understand why the other options are incorrect, we can look at their definitions within Nyaya logic:
- Asiddha: This is the fallacy of the unproved middle term, where the middle term itself is not established or is untrue.
- Satpratipaksa: This is the fallacy of the counter-balanced middle, where the middle term is contradicted by another middle term that proves the opposite of the major term.
- Badhita: This is the fallacy of the non-compatibly contradicted middle, where the middle term is contradicted by a stronger source of knowledge (like direct perception or testimony) other than inference.