whether gst payable or not?

No............., but ask supplier to issue the credit note for the same & return the goods on DC & CNT of suppliier

but when hospital is returning the product to the supplier it becomes a supply for hospital..ryt.?

Yes ... only case if Hospital is registered in GST.

so you are saying that your first answer is wrong.??

No .......
If you are registered in GST then at the time of purchase you must have claimed ITC , hence ITC is to Reverse when you are returning back to supplier.

As per Section 32 of CGST Act if you are not registered , you cannot claim ITC & reverse .ITC . (cannot collect & charge GST )

Note : As per Section 34. the supplier can issue credit or Debit in GST , so in case of Returning goods to supplier ask your supplier to Issue credit Note for the same .
(then even if you are unregistered , the supplier shall Reduce his output tax liability by issuing credit note )