In the following question, out of the four alternatives, select the word which is opposite in meaning to the given word. Impugnable.

Introduction / Context:
This antonym question focuses on a less common adjective used in formal and legal English. Impugnable is derived from the verb impugn, which means to challenge or attack something as false or questionable. Therefore, impugnable means capable of being attacked, questioned, or called into doubt. The candidate must select the option that most strongly expresses the opposite state, namely something that is not open to doubt or challenge.

Given Data / Assumptions:

• Key word: Impugnable.
• Options: Dicey, Debatable, Indubious, Hazy.
• We assume usage in contexts like arguments, claims, decisions, or evidence.
• The task is to choose the best opposite, not just a different word.

Concept / Approach:
Impugnable describes a statement, decision, or action that can reasonably be challenged or doubted. Therefore, the antonym must describe something that is beyond doubt or question. The option indubious, although less common than indubitable, is formed from in plus dubious and is intended in exam context to mean not doubtful or not open to suspicion. The other options dicey, debatable, and hazy all suggest uncertainty, risk, or lack of clarity, which are conceptually similar to impugnable rather than opposite. The correct approach is to recognise that indubious, by structure and meaning, denotes the absence of doubt.

Step-by-Step Solution:
Step 1: Understand impugnable as capable of being questioned, attacked, or doubted.Step 2: Examine Dicey. This means risky, uncertain, or of doubtful outcome, which implies that something is not secure and may be questioned.Step 3: Examine Debatable. This clearly means open to debate, dispute, or argument, which is very close to impugnable.Step 4: Examine Hazy. This means unclear or not well defined, again suggesting doubt and uncertainty.Step 5: Examine Indubious. By construction, this word means not dubious, that is, not questionable or not doubtful. This is the opposite state of impugnable, so it is the correct antonym.

Verification / Alternative check:
We can verify by substituting the words into a sample sentence. Consider The witness testimony is impugnable, meaning it can be challenged. If we switch to indubious, The witness testimony is indubious suggests that it is beyond doubt and cannot reasonably be attacked. Using dicey, debatable, or hazy in that place would only reinforce the idea that the testimony is unreliable or open to challenge, which does not create an opposite meaning. Thus indubious is the only option that reverses the sense of impugnable.

Why Other Options Are Wrong:
Dicey: This emphasises risk and uncertainty, which align with the idea that something could be challenged or may fail. It does not imply security or undeniability. Debatable: This directly indicates that an issue is open to argument, which is almost a direct synonym of impugnable. Hazy: This describes something unclear or vague, which again invites doubt. None of these words express the idea of being firmly established and free from suspicion.

Common Pitfalls:
Because indubious is less commonly encountered than dubious or indubitable, candidates may hesitate to pick it, even though the prefix in clearly marks it as a negative form. Some may also confuse dicey with decisive or debatable with reliable because they rely on approximate sound rather than precise meaning. A useful technique is to break words into parts: dubious means doubtful, so indubious naturally means not doubtful. Recognising these common prefixes can often unlock the answer in such vocabulary questions.

Final Answer:
The word that is opposite in meaning to impugnable is Indubious.