Final answer:
The missing type of Web site in the list provided is e-commerce. E-commerce sites are online platforms where goods and services are bought and sold, exemplifying the interactive and participatory nature of Web 2.0.
Step-by-step explanation:
The Thirteenth type of Web site to complete the list which includes portal, news, informational, business/marketing, blog, wiki, online social network, educational, entertainment, advocacy, Web application, content aggregator, and the missing type is e-commerce. E-commerce sites are platforms where consumers can purchase goods or services online, reflecting the participatory nature of Web 2.0 where users are not only viewers but also consumers. Platforms like Amazon are prime examples of e-commerce sites, allowing users to participate in online shopping, which has become one of the most significant aspects of the internet today.