Fill in the blank in the following sentence with the most appropriate…

The correct answer is Option (3) → unless

Conjunction of condition:

• Unless means "if not" or "except if"; it joins a condition to a main clause.
• It usually follows a negative idea: "not ... unless ..." means the action happens only when the condition is met.
• Deciding clue: the negative "not leaving", which needs an "if not" condition.
• This sentence: Rajesh does not leave the stage if he does not get a standing ovation, so "unless" joins the two parts.
• Complete sentence: Rajesh has a weird habit of not leaving the stage unless he gets a standing ovation.
  Example: I will not go unless you come with me.

Why the Other Options are Incorrect?

Option 1: because — Incorrect. Because gives a reason; it would say that he does not leave the stage because he gets an ovation, which is not the sense.
Example: She stayed at home because she was ill.

Option 2: as — Incorrect. As means while or since (because); neither gives the condition needed here.
Example: He smiled as he walked in.

Option 4: therefore — Incorrect. Therefore is an adverb that shows a result; it cannot join the two clauses, and a result makes no sense here.
Example: It rained all day; therefore, we stayed in.

Contrast: "unless" sets a condition (if not), "because" and "as" give a reason, and "therefore" shows a result.