Answer 1

Xamarin is a beautiful platform that focuses on developing apps for multiple platforms with a unified programming language (C#). 
I would recommend using it if you already have some knowledge in developing native applications. Also the native experience will help you in determining the usage of device oriented features such as network access, sensors etc.

On the other hand, Android studio is primarily built to develop Android applications with a lot of customized features such as templates, debug engine, abd and sdk integration etc.

If you want to get started with mobile development, I would recommend that you start with Android for a week ,understand the working of applications on the mobile platform and then switch to Xamarin for full scale development and implementation. (copied)