How often should Development Team members change?

Which of the following defines Elapsed Time?

A team member has made a mistake on a project. How should the scrum master address the mistake?

Stakeholders are unhappy because they have not been consulted on a user interface (UI) for a project that will have a significant impact on end users once it is launched. How should this situation be handled?

An organization wants to execute a corporate website redesign project using Scrum. There is an experienced pool of agile team members from a previous project, as well as a pool of available internal team members with some Scrum background. What should be considered when selecting the team?