Improve the underlined part of the sentence by choosing the most appropriate option: “The (reason of) her outburst at the party is yet unknown to anyone present.”

Introduction / Context:
This question checks knowledge of correct preposition usage with the noun “reason”. Such sentence improvement questions are common in competitive exams because many learners use incorrect prepositions due to direct translation from their mother tongue. The aim is to identify which phrase sounds natural and grammatically correct in standard English when describing the cause of an event like an emotional outburst at a party.

Given Data / Assumptions:

• Original sentence: “The reason of her outburst in the party is yet unknown.”
• The underlined phrase is “reason of”.
• We must select the most suitable replacement among the given options.
• We assume normal conversational and written English standards used in formal contexts.

Concept / Approach:
In English, certain nouns collocate naturally with particular prepositions. The noun “reason” is usually followed by the preposition “for” when we talk about the cause of an action, event, or feeling, as in “reason for his success” or “reason for the delay”. The phrase “reason of” is very rare and generally not accepted in standard formal English for this meaning. Prepositions “to” and “on” do not fit directly after “reason” in this sense. Therefore, “reason for” is the correct and idiomatic choice in this context.

Step-by-Step Solution:

Verification / Alternative check:
We can check usage by forming a few more sentences. For example, “Nobody knows the reason for his absence from the meeting” and “What is the reason for this delay” are clearly correct. If we replace “for” with “of” in such sentences, they sound awkward and non standard. The same logic applies to the sentence in the question. Professional writers, teachers, and high quality grammar references consistently prefer “reason for” when specifying the cause of an action. This independent check supports our choice.

Why Other Options Are Wrong:

• Option B: “reason to” is used in patterns like “reason to worry” or “reason to celebrate”, where it is followed by a verb. Here we have a noun phrase “her outburst”, so “reason to her outburst” is wrong.
• Option C: “reason on” is not a standard collocation in this sense. It does not occur in formal English to express cause.
• Option D: “No improvement” would keep “reason of”, which is not natural or idiomatic in standard grammar for this context.

Common Pitfalls:
Many learners rely on direct translation from regional languages, which often use a structure equivalent to “reason of” or “cause of”. While “cause of” is correct in English, “reason of” is not, so confusion arises. Another pitfall is ignoring collocations and only thinking in terms of dictionary meanings of prepositions. In exams, always recall how educated native and proficient speakers usually form such phrases: “reason for”, “cause of”, “effect on” and so on. Building a list of such common patterns can significantly increase accuracy in sentence improvement questions.

Final Answer:
The correct improvement is “reason for”, so the sentence should read “The reason for her outburst at the party is yet unknown.”