I have two site collections (A and B) belonging to the same content database. Inside site collection A there is a list "List1".. now i want to have the same list in the site collection B such - if there are any changes made to the list 1 in site collection A the same changes should b reflected in list1 inside site collection B - is this possible?
What kind of changes are we talking about?
If by changes you mean syncing of items, then you can simply write Item Receivers on List A for the
ItemUpdated events. When any of these events occur in List A, these receivers will open up SiteCollection B and inside that open up List B and do the necessary changes.
Here is a comprehensive guide on writing event receivers: