Custom screens in JIRA allow users to organize fields according to their workflow requirements. They are used to streamline the user interface by presenting relevant fields for particular operations, such as issue creation or transition. By creating custom screens, users can ensure that only necessary information is displayed, enhancing user experience and productivity.

The primary purpose of assigning an issue to a team member in JIRA is to ensure clear accountability and ownership. By assigning an issue, it becomes clear who is responsible for its resolution. This facilitates effective communication and coordination within the team, streamlining the workflow and ensuring timely resolution of issues.

In backlog management, "acceptance criteria" refers to the conditions that a product must satisfy to be accepted by the product owner. These criteria define the functional and non-functional requirements that must be met for a user story to be considered complete and ready for delivery. By establishing clear acceptance criteria, the team and the product owner align their understanding of what constitutes a successful implementation, ensuring that the delivered product meets stakeholder expectations and adds value to the end-users.

In JIRA, sub-tasks cannot have their own sub-tasks. They are meant to be smaller units of work that contribute to completing a parent task. Therefore, a sub-task cannot have further sub-tasks associated with it. Understanding this concept is crucial for managing task hierarchies effectively within JIRA.

The purpose of the "Rich Filter" gadget in JIRA Dashboards is to display a dynamic subset of issues based on predefined criteria. This gadget allows users to create complex filters to display only the relevant issues on the dashboard. It's particularly useful for teams that want to focus on specific aspects of a project or track progress based on custom criteria. With the Rich Filter gadget, users can tailor the dashboard to their specific needs and gain valuable insights into project status and progress.

Smart Values is a powerful feature in JIRA Automation that allows you to dynamically generate values for fields based on various parameters such as issue data, dates, and user information.

JIRA Service Desk distinguishes between request types and issue types by their respective purposes. Request types are used to categorize and manage incoming service requests, while issue types are used to classify tasks, incidents, and other work items within the system.

JIRA administrators can create custom Schemes to define unique sets of permissions for projects. Schemes in JIRA are configurations that allow administrators to control various aspects such as permissions, notification schemes, issue security, etc. They provide flexibility in defining specific configurations tailored to project requirements. Thus, option 3 is correct.

The correct option is Remaining Work. A Sprint Burndown Chart helps teams track their progress towards completing the remaining work in the sprint backlog. It shows how much work is remaining to be done as the sprint progresses, enabling teams to adjust their efforts and ensure they meet their sprint goals.

In JIRA, if a mistake is made during a bulk operation, the 'Undo' option can be used immediately after the operation to revert the changes. It's important to act quickly to ensure that unintended changes are undone efficiently.