In this single word substitution question, you are asked to choose the verb that best expresses the meaning of the phrase to officially register as a member of an institution. Read the options carefully and select the one that matches this idea in standard English usage.

Introduction / Context:
This question belongs to the category of single word substitution, where a longer phrase is replaced by a single, precise word. The phrase given is to officially register as a member of an institution, which refers to the act of getting one's name recorded in the official list of members or students of a college, school, club, or similar organisation. Being able to select exact verbs for such actions is important for clear, concise communication and is frequently tested in competitive exams.

Given Data / Assumptions:

• The phrase to be replaced is to officially register as a member of an institution.
• The options given are to muster, to enrol, to institutionalize, and to officiate.
• The intended context includes joining a college, course, society, or club.
• Only one verb matches this meaning accurately in common English usage.
• You must select the option that a native speaker would naturally use.

Concept / Approach:
The action described is that of joining an institution by completing formal registration procedures. The common verb for this is enrol in British spelling or enroll in American spelling. It means to be officially recorded as a member or student. The other verbs have different meanings. muster means to gather people, usually for inspection or a meeting. institutionalize means to make something part of an established system or institution, often used in abstract contexts. officiate refers to performing official duties, such as conducting a ceremony or supervising a match. None of these expresses the idea of registering oneself as a member.

Step-by-Step Solution:
Step 1: Read the phrase carefully: to officially register as a member of an institution. Imagine a student filling out forms to join a college or a person signing up to become a club member. Step 2: Consider option to muster. This usually means to gather people together, for example to muster troops. It does not mean to register as a member. Step 3: Consider option to enrol. This verb directly means to register or enter someone's name on a list, especially in a school, course, or organisation, which matches the phrase exactly. Step 4: Consider option to institutionalize. This means to establish something as a normal part of an organisation or social system, which is unrelated to a single person joining an institution. Step 5: Consider option to officiate. This is used when someone performs a formal duty at an event, such as officiating at a wedding or officiating in a sports match. It does not mean to register as a member. Step 6: Since only to enrol accurately captures the sense of officially registering as a member, it must be the correct answer.

Verification / Alternative check:
Think about how the phrase appears in real sentences. We often say Students enrol in the first semester, or She enrolled in the new management programme. We do not say She mustered in the college or She officiated in the course when we mean that she registered as a student. This confirms that to enrol is the correct single word substitution.

Why Other Options Are Wrong:
to muster is about gathering people, especially soldiers, and does not denote registration.
to institutionalize refers to embedding a practice or idea within an institution, not an individual joining that institution.
to officiate refers to carrying out formal duties at an event and is unrelated to membership registration.

Common Pitfalls:
Students sometimes confuse institutionalize with enrol because both contain the root institution, but their meanings are different. Another pitfall is focusing only on formal sounding words rather than checking whether the verb really fits the described action. It is safer to recall or construct simple example sentences to test each option in context, which quickly reveals the correct choice.

Final Answer:
The verb that best expresses the idea to officially register as a member of an institution is to enrol.