Which application will allow a client to enable Ideas on a public website?

The correct choice is C, as Salesforce Sites allows organizations to create public websites that can be linked to their Salesforce data. When using Sites, clients can enable the Ideas functionality, making it accessible to external users. This feature is particularly beneficial for gathering customer feedback and suggestions directly on a public-facing site, thus facilitating community engagement and idea management without requiring a Salesforce login.

By using Sites, businesses can customize their online presence while managing ideas and contributions efficiently through the Salesforce platform. This capability enhances the ability to interact with customers, gather insights, and foster collaboration.

The other portals mentioned, such as the Partner portal, Self-service portal, and Customer portal, are designed for users who have authenticated access, thus limiting their use to those who already have a Salesforce account. They do not support public-facing features for collecting ideas from non-registered users, which is a primary function of Sites.