The section of the Act that makes a representation inadmissible if action was taken on its direction is:

This question delves into the rules of admissibility within legal or administrative proceedings. Section 39 of the Act is critical as it stipulates that a representation becomes inadmissible if action has already been taken based on its direction. This provision prevents parties from making a representation, acting upon it, and then later attempting to challenge or retract it, thereby maintaining the integrity of the process and preventing abuse.

• Option A (36) relates to enforcement for non-compliance.
• Option B (38) deals with movable encroachments.
• Option D (40) governs the delivery of notices and orders.

Therefore, 39 is the correct section concerning the inadmissibility of representations.