How to Check Oracle Database and SYNC status ?

 
select name,open_mode,database_role from v$database;

select pr.thread# "Node", pr.primary "Primary",dr.Standby "DR",pr.primary-dr.Standby "Difference"
from (select thread#,max(sequence#) as primary from v$archived_log where
resetlogs_change#=(select resetlogs_change# from v$database) group by thread#) Pr,
(select thread#,max(sequence#) as Standby from v$archived_log where
resetlogs_change#=(select resetlogs_change# from v$database) and applied='YES' group by thread#) dr
where pr.thread#=dr.thread#;