Pick the most effective word from the given options to fill in the blank and make the sentence meaningfully complete: The unruly behaviour of the soldiers _____ their commander.

Introduction / Context:
This vocabulary question checks how accurately you can choose a verb that expresses a very specific emotional reaction. The sentence talks about unruly behaviour by soldiers and the reaction of their commander. You need a word that means made someone extremely angry or furious. Knowing the fine differences between verbs like clash, aggrieve, impeach and incense is important for scoring well in competitive English exams.

Given Data / Assumptions:
The sentence is: The unruly behaviour of the soldiers _____ their commander.
Subject causing the reaction: the unruly behaviour of the soldiers.
Person affected: their commander.
We need a past tense verb that correctly describes the effect of that behaviour on the commander.
We assume the commander feels strong anger or outrage at indiscipline in the ranks.

Concept / Approach:
The approach is to interpret the emotional tone implied by unruly behaviour. Such behaviour does not usually cause mild sadness or formal charges in this kind of one-line sentence; it normally provokes anger or indignation. The verb we choose should therefore mean made very angry. Incensed, used as a verb in the past form, precisely means caused to be extremely angry. The other options either describe different actions (such as formally charging someone) or do not fit the emotional context properly.

Step-by-Step Solution:
Step 1: Read the sentence with each option inserted and check meaning and grammar. Step 2: The unruly behaviour of the soldiers clashed their commander is incorrect, because clash is usually intransitive or used with with, as in clashed with their commander. Step 3: The unruly behaviour of the soldiers impeached their commander is wrong, because impeach means to formally charge a public official with misconduct; the soldiers behaviour is not charging the commander. Step 4: The unruly behaviour of the soldiers aggrieved their commander seems possible grammatically, but aggrieved usually suggests making someone feel wronged or treated unfairly, not primarily furious at indiscipline. Step 5: The unruly behaviour of the soldiers incensed their commander means it made him extremely angry or enraged, which fits both the emotional intensity and the military context. Step 6: Therefore, Incensed is the most effective word to complete the sentence.

Verification / Alternative check:
You can quickly test collocations. We commonly say someone is incensed by bad behaviour or incensed at an insult, clearly linking to anger. By contrast, impeach takes an object like president or minister and usually appears with formal context, while clash typically appears as clash with someone or clash over an issue. These patterns confirm that only incensed naturally describes the commanders reaction to unruly soldiers.

Why Other Options Are Wrong:
Clashed suggests a mutual conflict, often between two sides, not a one-way emotional reaction caused in a commander by someone else behaviour.
Impeached refers to a legal or constitutional charge, not an emotional response, so it does not match the idea of behaviour upsetting a superior officer.
Aggrieved emphasises feeling wronged or unfairly treated rather than being enraged by insubordination, so it is weaker and less precise than incensed here.

Common Pitfalls:
A common mistake is to pick a word that vaguely sounds negative without checking its exact meaning and normal usage. Exam questions often include near misses that are grammatically possible but semantically off. To avoid this, always ask: what exact emotion or action is being described? In military discipline, unruly behaviour typically provokes strong anger, making incensed the best match.

Final Answer:
The correct and most effective word is Incensed.