A . Junction object between Applicant and Job:
Since an Applicant can apply for multiple Jobs and each Job can have multiple Applicants, this is a many-to-many relationship.
Salesforce requires a junction object to represent many-to-many relationships. The junction object will have two master-detail relationships: one to the Applicant object and one to the Job object.
The junction object could be named something like JobApplication__c, which would represent the specific instance of an applicant applying for a particular job.
Why this is the correct approach?
A junction object allows for robust data management and reporting capabilities in a many-to-many relationship.
This design ensures that each combination of applicant and job is captured as a unique record in the JobApplication__c junction object.
It also allows storing additional details about the application, such as application date, status, and feedback.
Why not the other options?
B . Lookup field from Applicant to Job:
A lookup field creates a one-to-many relationship. While an Applicant could reference one Job, it does not support the many-to-many relationship required in this scenario.
C . Master-detail field from Applicant to Job:
A master-detail relationship is a one-to-many relationship, which is unsuitable for a many-to-many relationship. Additionally, you cannot have two master-detail fields on a single object to connect Applicant and Job directly.
D . Formula field on Applicant that references Job:
A formula field cannot establish relationships between records or represent a many-to-many relationship. It is only for computed fields.
Reference:
Creating Many-to-Many Relationships with Junction Objects
Master-Detail and Lookup Relationship Details