I have core 2 duo 2.80 ghz with zotac 1 gb graphic card and 2 gb of ram and I want to play assassin creed 4 black flag. Can I

Solution
You're going to need a lot more info than just your processor speed. Check your GPU, VRAM and RAM too. A lot of times it depends more on your GPU than your CPU.
Assasins creed 4 is well playable with core2duo If paired with a decent card. You will see fps drops more because of your processor and lowering the settings in this case won't help too because gpu might be bottlenecked by the cpu