Option A: An External ID field can be used to reference an ID from another external system.
True.
External IDs are custom fields that have the External ID attribute selected.
They are used to store unique identifiers from external systems, allowing Salesforce to match and integrate data based on external IDs.
External ID fields are automatically indexed, which means they can improve the performance of SOQL queries, especially when used in the WHERE clause.
Indexed fields reduce query times on large datasets.
External IDs do not make external data visible in Salesforce or Salesforce Mobile.
To make external data visible, you would use features like Salesforce Connect.
Formula fields cannot be marked as External IDs.
Only Text, Number, Email, or Auto-Number fields can be designated as External IDs.
Reference:
External ID Fields
Option B: External ID is indexed and can improve the performance of SOQL queries.
True.
Custom Indexed Fields
Option C: An External ID can be used with Salesforce Mobile to make external data visible.
False.
Salesforce Connect
Option D: An External ID can be a formula field to help create a unique key from two fields in Salesforce.
False.
Considerations for External IDs
Conclusion:
The correct benefits of using External IDs are A and B.