The Scrum Master’s key responsibility when estimating stories is to ensure that everyone on the team participates in the process. This is aligned with the Scrum Master’s role as a facilitator and servant leader, who must encourage full team engagement to leverage the collective expertise and perspectives of all team members. This helps in creating more accurate and reliable estimates and promotes team ownership of the tasks.

Here’s a detailed breakdown of the Scrum Master’s role during story estimation:

Facilitation: The Scrum Master facilitates the estimation process, ensuring that it is collaborative and that every team member has the opportunity to contribute1.

Encouraging Participation: It is crucial that all team members participate in the estimation to provide diverse insights and reach a consensus on the effort required for each story1.

Coaching: The Scrum Master also coaches the team in estimation techniques and helps them understand the value of collective estimation as part of the Agile process2.

Maintaining Agile Principles: They guide the team in adhering to Agile principles during the estimation process, ensuring that the team remains focused on delivering value efficiently2.

The other options (A, C, D) are not the primary responsibilities of the Scrum Master during story estimation. While the Scrum Master may support the team in achieving accurate estimates and managing time effectively, their key responsibility is to ensure active participation from all team members, which is fundamental to the Agile methodology and the Scrum framework3.