Answer:   If the parent objects don’t have Roll up Summary fields for the child object then we can delete. To delete a child object it should not be referred in Apex Classes and Apex Triggers. Later if we undelete the object, Master detail fields on the junction objects will be converted to look up Fields.
Note: If we delete only Master – Detail Relationship field from the child object and undelete it from the Recycle Bin then it will be converted to look up relationship. Parent Object we cannot delete because it will be referred in the child object.