How to get a Memory address of the Object?

Physical memory addresses are non-existant for applications in protected mode. This is a privileged operation that you as application do not have. You would also get nothing by simply reading physical addresses because you should also know what is on that physical address and due to paging that varies from time to time. The OS won't let you get in the way there and would be considered an security risk.

Well, you can do that. The keywords you should look for are "pointer pinning", "unsafe mode" and in general, "pointers in the managed run-time". But you have to be aware of the side effects of this - the Answer 1 already gives you a hint. Before you start working with pinned pointers and "unsafe" statements you should really answer the the question already asked above: "What are you trying to accomplish?" Pinning is rarely needed and I would strongly recommend to find another way...

You can (without unsafe code) create a pinned GCHandle (and it must be pinned), then call AddrOfPinnedObject to get an IntPtr, which is the address of "that particular object". Optionally turn it into a pointer or long (preferably not an int)
But yes, what are you doing?

GCHandle objHandle = GCHandle.Alloc(YourObject, GCHandleType.WeakTrackResurrection);