What can be used to share a single record of a custom object with an Employee site user?

Manual Sharing is the correct choice for sharing a single record of a custom object with an Employee site user because it allows specific records to be shared on a case-by-case basis. This feature is particularly useful when you want to grant access to a specific record to certain users without changing the overall sharing rules for the entire object.

When using Manual Sharing, the owner of the record can explicitly choose which users should have access to that particular record, and this access can include different permissions such as read-only or read/write. This granularity is important in scenarios where sensitive data is involved or when access needs to be limited for compliance or business reasons.

In contrast, other options may not fit the scenario effectively. Team Sharing is typically used for sharing sets of records with a defined team based on roles rather than individual users. Public Access involves making records available to all users of a site and is not tailored to individual needs. Dynamic Sharing is a more complex option that involves automated sharing rules based on specific criteria but would not allow for the manual specification of access for a single record.