Oracle Active Data Guard - OPEN_MODE STATUS
When working with DataGuard, I would strongly advise using the DataGuard Broker (dgmgrl).  

It greatly simplifies the cluster management process and is the tool of choice for interrogating and diagnosing problems with the cluster. 

dgmgrl / 
DGMGRL&gt; show configuration
. . . 
DGMGRL&gt; show database PRIMARY_DB
. . . 
DGMGRL&gt; show database STANDBY_DB
. . .