Although the Stakeholder(s) and the Product Owner have the final say on Prioritized Product Backlog Items and whether to accept or reject any Change Requests presented during Demonstrate and Validate Sprint, it is the Scrum Master's responsibility to ensure that the requirements and Acceptance Criteria are not altered during the Sprint Review Meeting for the User Stories completed in the current Sprint. This prevents the rejection of completed User Stories based on the fact that they do not meet newly changed requirements. If any requirements need to be changed, any corresponding PBI needs to be revised to accommodate the modified requirements in a future Sprint.
Reference: http://blog.scrumstudy.com/change-management-in-scrum-framework/

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 Reference:
https://www.knowledgehut.com/interview-QUESTION NO:s/scrum

Reference:
http://blog.scrumstudy.com/exploring-the-implement-phase-of-a-scrum-project/

An important tool which can be used for communicating information related to risks is the Risk Burndown Chart.