in my code

List<Student_Batch_Junction__c > c=new List<Student_Batch_Junction__c>([select Student__r.id from Student_Batch_Junction__c where Batch__r.Name in :b]);

variable c contains:
11:55:42:011 VARIABLE_ASSIGNMENT [11]|this.c|[{"Student__c":"a022v00001GmqnrAAB","Batch__c":"a042v00002CobkCAAR","Id":"a052v00000l4WxtAAE","Student__r":{"Id":"a022v00001GmqnrAAB"}},{"Student__c":"a022v00001GnNHiAAN","Batch__c":"a042v00002CobkCAAR","Id":"a052v00000l4c5dAAA","Student__r":{"Id":"a022v00001GnNHiAAN"}}]

I want to get only Student__r id field values.
how to get that?