* Why External ID?
* The Order Number is used to identify records uniquely, both in Salesforce and in external systems.
* Marking it as anExternal IDensures it can be matched or referenced during data imports and integrations.
* Why Unique?
* Setting the field as Unique ensures that duplicate values are not allowed for the Order Number.
* Why Not Other Options?
* A. Indirect Lookup: Used for external object relationships, which is not applicable here.
* B. Direct Lookup: Not relevant for unique field identification.
* D. Lookup: Used for creating relationships, not for identifying unique fields.
References:External ID Field:https://developer.salesforce.com/docs/atlas.en-us.object_reference.meta/object_reference/field_types.htm