Web based captive portal can be authenticated by the following types of databases:

The choice indicating "Internal" databases as an option for authenticating users on a web-based captive portal is correct because internal databases are specifically designed for managing user credentials and profiles directly within the networking device or controller itself. This kind of authentication is typically used for simpler, smaller environments where deploying an external directory service is not feasible or necessary.

An internal database allows for straightforward user management, as it maintains user information such as usernames and passwords locally, enabling immediate access and authentication for users connecting to the network. This approach can effectively streamline the authentication process without the additional complexity that might come from integrating with external systems.

While external databases like LDAP, RADIUS, or MySQL can also be employed to authenticate users on a captive portal, the question specifically highlights the internal option, focusing on its applicability and use cases in managing user access directly within the network infrastructure.