Final answer:
The agency fund is the fund where assets always equal liabilities because it acts as a custodian for assets that belong to external parties.
Step-by-step explanation:
The fund that has no net position, where assets always equal liabilities, is the agency fund. Unlike other funds such as private-purpose trust funds, pension trust funds, and investment trust funds, the agency fund solely acts as a custodian for assets that are held on behalf of others and does not have a net position on its own. Any resources held by an agency fund belong to external parties, and the fund's liabilities to those parties are equal to the assets it holds. This is analogous to situations in government finance where one part of the government owes money to another, like debt held by government trust funds rather than the public.