"For" is used to indicate a duration of time. The sentence means the property should not be sold for the next three days, making "for" the most appropriate preposition.
I request you to not sell the property ___ three days
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Question context
This question is part of 🗣️ Verbal Ability within the broader 🧠 Aptitude Mastery subject and appears in the Education Testing Council by HEC preparation collection. Reviewing the answer together with nearby questions helps reinforce the underlying concept and identify how it may appear in competitive exams.