1.Is it manadatory to have it in archive log mode ?
Only if you switch the its role to Primary.
2.As it is in archive log mode , does it produce any archivelog ?
In the "PRIMARY" role it must produce archive. Otherwise Data Guard cannot and would not work correctly if you do a switchover or failover.
SELECT DATABASE_ROLE FROM V$DATABASE;
Its does not produce archive in the Standby role. I have seen a Standby produce a log now and then, but not log after log like a primary. A Standby database does not write Redo or use Redo logs, it uses Standby Redo logs. Since Redo logs are not used, archive is not written.
Why does it need to produce archive in standby role?
Smart design I'm thinking. Why would Oracle make us add this complex step to a failover/switchover?
Why it is manadatory to enable archive log in standby?