Explanation
When an administrator deletes a custom field, Salesforce moves it to the deleted fields list for 15 days, during which time it can be undeleted or erased permanently. If the administrator undeletes the field within 15 days, most of its properties and data are restored, except for its field history data, which remains deleted and cannot be recovered. References: https://help.salesforce.com/s/articleView?id=sf.custom_field_delete.htm&type=5

Explanation
A restricted picklist is a type of picklist that enforces the integrity of the picklist values by allowing only values defined inthe picklist during data entry or import operations. If the restricted picklist checkbox is checked for a picklist field, then any records with values not defined in the picklist will cause errors during import operations. However, if the restricted picklist checkbox is unchecked for a picklist field, then any records with values not defined in the picklist will be imported without errors.
References:https://help.salesforce.com/s/articleView?id=sf.picklist_limitations.htm&type=5

Explanation
The Knowledge Lightning component is a component that allows users to access articles fromthe Service Cloud Console app. However, if users want to access articles from a different app that does not use the console, they can use the Knowledge related list instead. The Knowledge related list shows articles related to a record based on data categories and shows article details such as title, summary, rating, and view count. To add the Knowledge related list to a record page, an administrator can use the page layout editor and drag and drop the Knowledge related list to the appropriate section on the page layout. References:
https://help.salesforce.com/s/articleView?id=sf.knowledge_lightning_component.htm&type=5https://help.salesfo