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/

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

Explanation
Because stakeholders have an interest in the project, it is important to communicate with them regarding risks.
Information provided to stakeholders related to risk should include potential impact and the plans for responding to each risk. This communication is on-going and should occur in parallel with the four sequential steps discussed thus far-risk identification, assessment, prioritization and mitigation. The Scrum Team may also discuss specific risks related to their Tasks with the Scrum Master during Daily Standup Meetings. The Product Owner is responsible for the prioritization of risks and for communicating the prioritized list to the Scrum Team. An important tool which can be used for communicating information related to risks is the Risk Burndown Chart.

Reference:
https://katherinemichel.gitbooks.io/agile-sprint-playbook/project-management/scrum-body-ofknowledge- phases.html