since , here, roll no is primary key is given for both the table not any clue about foriegn key is given so, we cant assume ROLL as foreign key.
suppose a condition:-
then , if we apply natural join(*) hen no any tuples will be selected
now for aximum,
suppose a condition where all the 8 tuples in ENROLL is present then STUDENT(naturaljoin)ENROLL gives 8 tuplesbecause out of 120 tuples only 8 tuples will be matched
and, since , roll no. os student table is also PK then they must be differnt so maxm * tuples
so, final answer must be 8,0
but, in option it is not given so, i think GATE question setter have missed out to mention refrencial integrity . if, RI would be there then it's answer will be 8,8