Select the antonym (word opposite in meaning) of the verb phrase "to muster".

Introduction / Context:
This question asks for the antonym of the verb to muster. In many contexts, to muster means to gather together people, courage, or resources, especially for a particular purpose such as a battle, a meeting, or a challenging task. The antonym must therefore express the opposite idea: breaking up, separating, or alienating rather than assembling.

Given Data / Assumptions:

- Target verb: to muster. - Options: to convocate, to rally, to estrange, to aggregate. - The usual contexts include mustering troops, mustering courage, or mustering support. - The correct antonym should involve separation or alienation instead of gathering.

Concept / Approach:
To muster often overlaps in meaning with to gather, to assemble, or to rally. Three of the options, convocate, rally, and aggregate, all relate to bringing people or things together. The only option that implies distancing or breaking relationships is to estrange, which means to cause someone to feel less close or no longer friendly. Although estrange is not a perfect dictionary opposite of muster, it is the only option that moves in an opposite direction conceptually.

Step-by-Step Solution:
Step 1: Recall typical usage: The commander mustered the troops or She mustered the courage to speak. Step 2: Notice that in all such examples, muster is associated with bringing together forces or feelings. Step 3: Examine to rally, which clearly means to come together again, especially in support of a cause, and so is similar to muster. Step 4: Consider to convocate, which is related to convene or call people together for a formal meeting, another gathering verb. Step 5: Look at to aggregate, which means to collect into a mass or whole and is again close to assemble. Step 6: Study to estrange, which means to make someone no longer close or affectionate, often leading to separation or isolation, the opposite tendency of bringing together.

Verification / Alternative check:
Imagine parallel sentences with a contrast. If a leader musters support, he is gathering supporters; if he estranges his supporters, he is driving them away. Similarly, a family can muster the members for a reunion or estrange them through conflict. In this way, muster and estrange can be seen as opposite actions affecting group unity, whereas convocate, rally, and aggregate all help unity rather than weaken it.

Why Other Options Are Wrong:
To convocate is closely linked with convening or calling a formal meeting, which brings people together and is similar to muster. To rally also means to organise or gather people to support a cause, directly parallel to muster support. To aggregate describes collecting items or data into one whole, again reinforcing the idea of gathering. None of these verbs express separation or alienation, so they cannot be antonyms of muster.

Common Pitfalls:
Because muster is often seen in military or formal contexts, some students may be tempted by convocate or rally as answers simply because they feel technical. However, the question asks specifically for an antonym, not a synonym. A useful strategy is to first say a simple synonym in your own words, such as gather, and then look for a verb that instead means separate or push apart. Estrange is the only option that matches this reversed direction.

Final Answer:
to estrange is the best available antonym of to muster among the given options.