Hi,
Is it legal to play artist pop song piano version in my app?
Will I get banned by google play?
Thanks.
It doesn’t matter whether artist is popular or not.
There are licences and they apply to everyone.
If song is licensed under licence that allows you to use it in commercial purposes then it’s fine. However if it’s not then yes, it’s a copyright infringement.
Check out Creative Common Licences (3.0 , 4.0 especially those).
Edit: But be careful, sometimes happens that people use other artists songs and claim them as their own. Or sometimes artists will licence their work under CC by 3.0 and still not be okay with you using their work in certain way. And sometimes they just want to be asked but thats very rate since the purpose of these licences is to not ask. But they can set the rules so…
If you don’t own the copyrights don’t try to use it. There is a copyright law for intellectual property which may trouble you,but keep in mind there are some websites that can give you free for commercial music just google it and see 
Ad. 1. No.
Ad. 2. Yes.
First thing you do in the morning - read up on copyright law. You shouldn’t have to ask such question, it’s obvious.
You should use music under free commercial licence otherwise it is illegal.