connect to specific wifi only I want my device to be connected to a certain wifi network only. Lets assume  WiFi named "xyz": so my device should connect to this particular "xyz" network only. It Should not connect to any other network.

More precisely: I don't want other user's to use my device with any other WiFi network. Basically I want to restrict user to access other network.

My device is rooted, so can I achieve this by doing some settings at OS level?
AFAIK there's no such "OS setting" (and if there was, "other users" could manipulate it as well).

As a "work-around", you might look in the Playstore for app lockers, they should be able to "lock" the settings app as well. Remove all WiFi APNs from your network list which should not be connected, de-Activate the "inform me about open WiFi networks" to avoid the popup, and together with an app locker (locking the "settings" app) that should do what you're looking for.

As to your comment, this seems to work fine with Smart AppLock, which can lock not only apps but also some system actions:

 
Smart AppLock: Locking apps, locking system actions (source: Google Play; click images for larger variant)