Alright for level 4 here are some more hints:
Yes, tin is the missing element. Now, i have given hints already through the thread. i'm not just gonna give you the answer. Now, there is a place somewhere in the vicinity of Shanghai that has some relationship with the fact that there is no tin. you just need to find the place and you'll know when you have it. Try wikipedia.
As for me, I'm stuck on five.