The reason behind asking this question is that for almost all the things in oracle there is hard limit so i thought what would be the hard limit for Listener ...??

I am asking this question for my knowledge purpose.

As said listener in hard sence is not bound to the db. So I think there is a problem of words.
You could say Listener instances instead.

Sometimes say For maintenance reasons, it could happen to separate the access of different applications bases. For this, we must define two instances of listener. Here is an example of such listener.ora (1 listener for the instance of the database of the appli 1 and a listener for both databases instances of the appli 2):

LSN1 =
(ADDRESS_LIST =.......
(ADDRESS = (PROTOCOL = TCP) (Host =
...
LSN2 =
(ADDRESS_LIST =
)

So, to start a listener specify the instance:
> Lsnrctl start LSN1
> Lsnrctl start LSN2
and
> Lsnrctl stop LSN1
> Lsnrctl stop LSN2

Yogesh,
Since you asked the question to add to your knowledge, here is link to documentation on Oracle limits:

http://docs.oracle.com/cd/E11882_01/server.112/e40402/limits.htm#REFRN004

As you can see there is no limit to the number of listeners from an Oracle perspective. However, there are practical considerations which dictate that we limit the number of listeners on a server.

Also, listeners are not tied to a database as Connor said. One listener can listen for multiple databases. I strongly encourage you to read about how listener works here:

http://docs.oracle.com/cd/E11882_01/network.112/e41945/listenercfg.htm#NETAG010