The prime responsibilities of a Scrum Master are:

Removes the obstacles/impediments that affect productivity.

Shields the people from external disturbance.

Responsible if the scrum process is correctly applied.

Facilitate daily stand-ups, other ceremonies, schedule meetings, demo and other meetings.

Help product owner in prioritizing the backlog and any feedback from the team.

Facilitation of Retrospective meetings

Workshops for planning, estimation, prioritization, issue resolution, performance improvements