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

Section 25 is typically the section in revenue laws that specifically outlines the 'mode of service' for notices or orders. This section details the various methods, such as personal delivery, registered post, or affixing the notice, ensuring that all parties are properly informed and due process is followed in revenue proceedings.

• Sections 23, 24, and 26 would address other distinct aspects of the law, such as the issuance of notices, powers of officers, or specific procedures, but not the detailed methods of service itself.