Which plugin is used to play .mp3 among them?

I removed libxine1 but still can run .mp3 with amarok.
rpm -qa | grep gstreamer


Which plugin is being used to play .mp3 among them?

If i do rpm -qa | grep ffmpeg it displays nothing.

you need plugins-bad

any reason why you removed xine and replaced it with gstreamer? I’ve no issues with Packman packaged libxine and playing mp3’s in amarok

Some basics …

openSUSE as packaged by Novell/SuSE-GmbH is crippled for proprietary audio such as mp3. The nature of the crippling is such that just removing an application is not going to provide the needed codec. Hence removing the Novell/SuSE-GmbH packaged libxine1 will not accomplish what you seek. A better approach would have been to replace the Novell/SuSE-GmbH packaged libxine1 with a Packman packaged libxine1.

Here is a new user guide/how-to for you to read:
Multi-media and Restricted Format Installation Guide - openSUSE Forums

Without gstreamer-plugins-bad , amarok still can play .mp3 files.

That was gst-fluendo-mp3.
This is the plugin to play .mp3 files with amarok.