What are the chemical compositions of human brain and kidney ?
I need to know the composition percentage of each chemical element .Thanks.

What do you think they are? We aren't going to do your homework for you.

It's not my homework. I need it for my project and I can't find it in the internet.

Well if you can't, we probably can't too.

If you put that into Google exactly how you stated it here, you will get some answers, and probably one you can pick that will be suitable, assuming of course you know your course data.