The section dealing with mode of service of notice or order is:

Section 25 is the correct answer. In legal and administrative acts, Section 25 typically specifies the precise procedures and methods for serving notices or orders to ensure that all concerned parties are properly informed. This section is crucial for upholding due process and the legal validity of communications.

• Section 24, Section 26, and Section 23 would address other distinct provisions within the relevant statute, such as powers, duties, or other procedural aspects, but not specifically the mode of service of notice or order.