I was using Nokia E51 earlier. When I pressed "Menu" key for a few seconds, it displayed all the "Running Programs", which helped me to close down and save Battery.

Is it possible in BB Pearl 8120 to know which program is running and shut them down for saving battery purpose and all that?

Not sure if the model supports this way, but try pressing ALT and the back key (arrow, left of end call key). You need to hold Alt, then scroll left or right to see whats running.
Once on an application, stop holding ALT and it will go to that application.

Note, 5 applications are always running and cannot be shut down.
Messages, Phone, BB Messenger, Home, and Browser.

Thanks, it worked on my 8900. I didn't know I had all of those open.

Make sure you close apps and not just exit out.

I am using BB 8120. Would u mind to tell which is ALT button? It has half-qwerty keyboard. and it also has no arrow keys.

I already explained where the back key is.
It looks like a curving arrow and is: left of end call key. Or right of trackball.

Not idea about ALT though.

Wirelessly posted (L'neuf trois)

The ALT key on the 8120 is located on the bottom row of keys, farthest to the left. It is appropriately labeled "ALT."

When I press the mentioned keys, Language Menu opens.