Answer: Scrum Master is provided with responsibilities for ensuring that his/her group actively follow intelligent belief and value, also pondering onto the fact that the group follows the operation and practices agreed upon.
Their roles mostly encompasses the following:
(a) removing hindrance for his/her team, so they can work smoothly.
(b) Providing his/her team with surroundings where they can be effective.
(c) Addressing group dynamics whether it is intra-group or inter-group.
Here, in this particular case we have two candidates:
1. Mary knows Scrum very well, but she's very young and has no real world experience.
2. Mark doesn't know Scrum, but has eight years of experience in managing IT projects.
So, in this case Mary is a better choice for the role of Scrum Master because she knows Scrum and she will learn project management soon.