In Scrum, the product owner is responsible for maximizing the value of the product by managing the product backlog. This includes prioritizing requirements, refining backlog items, and ensuring that the development team works on the most valuable features first.
Option A: Velocity metrics are typically monitored by the Scrum Master and team, not the product owner.
Option B: Burndown charts are updated by the team, not managed by the product owner.
Option D: Assisting developers with coding and blockers is the responsibility of the Scrum Master and development team.
Thus, the product owner's main responsibility is to prioritize requirements and manage the backlog.
Reference:
WGU Information Technology Management - Agile and Scrum Practices, section on Scrum Roles: Product Owner.