How do I: Activate - deactivate instances

Hi

I have a problem in my game.

I have two instances of the same object (eg. Dog).

I wish that when I click with the mouse on the dog object, instance 0, this instance would change opacity to 50 (ok, that I can get it).

Then I would like that when I click with the mouse on the dog object, instance 1, this instance changed the opacity to 50 and simultaneously the instance 0 returned to opacity 100.

Is it possible ?

Thanks

Thanks for the quick reply. It works fine.