Explanation:

Let's break down the options for you:

- Order 5, Rule 13:

- This rule in the Code of Civil Procedure (CPC) deals specifically with service of summons on an agent through whom the defendant carries on business.

- This is typically used when the defendant is not easily reachable, but conducts business through an agent.

- Order 9, Rule 12:

- This rule pertains to the procedure on the granting of ex-parte decree and the setting aside of the same.

- It is not related to service on an agent.

- Order 6, Rule 10:

- This rule provides for the particulars necessary in a pleading. It outlines the need for specificity in legal documents.

- This rule does not address service procedures.

- Order 10, Rule 8:

- This rule deals with the first hearing of a suit and the examination of parties by the court.

- It is unrelated to service on an agent.

Order 5, Rule 13 is the correct answer.