An Infrastructure Administrator is a role in NDB that has the permission to manage network and storage resources, such as VLANs, IP Pools, and Storage Containers. This role is suitable for the engineer who needs to add new VLANs or IP Pools in NDB. The other roles have either more or less privileges than required for this task. A Database Administrator can manage databases and database server VMs, but not network and storage resources. A Super Administrator can manage all aspects of NDB, but this is more than the least-privilege access needed. A Database Infrastructure Administrator can manage both databases and network and storage resources, but this is also more than the least-privilege access needed.
References: Nutanix Support & Insights, section "NDB Roles and Permissions"

Point in Time Recovery (PITR) is a feature of NDB that allows restoring a database to any point in time within the retention period of the SLA. To enable PITR, the SLA must support Continuous Log retention, which means that NDB captures and stores the database logs continuously. This allows NDB to replay the logs from the last snapshot to the desired point in time during the restore process. The other options do not enable PITR, but rather affect the frequency and timing of the snapshots and log catch up operations.
References: Nutanix Support & Insights, section "NDB Time Machine Point in Time Recovery"

The administrator can remediate the issue of critical storage alerts by scaling up the storage directly from the Database Summary page for that specific DBA database. This action allows for an increase in storage capacity to alleviate space constraints and prevent future critical alerts related to storage space1. The other options are not correct, as they either involve scaling the entire database group, which may not be necessary or desired, or require additional steps outside of NDB, which may not be feasible or efficient. References:
* 1: Nutanix Database Automation (NCP-DB) course, Module 2: Database Provisioning, Lesson 2.4:
Database Scaling, slide 5

Nutanix Era offers Role-Based Access Control capabilities by organically embedding them in the product. It provides the ability to add and remove users from Era, create and assign roles to users, and associate various privileges with a role1. The default roles available within Era for Role-Based Access Control are:
* prism Admin
* Era Super Admin
* Era Database Admin
* Era Infrastructure Admin1 These roles allow for the management of both physical resources like IP addresses and VLANs along with database entities like databases, time-machines, clones, and so on1.

To roll back an Oracle patch on a database server VM using NDB, the patch must have been applied using NDB in the first place. This is because NDB maintains a patch inventory and history for each database server VM and database that it manages. NDB uses this information to determine which patches can be rolled back and how to revert the changes made by the patch. If the patch was applied outside of NDB, NDB would not have the patch information and would not be able to roll back the patch. Therefore, the patch must have been applied using NDB for the rollback action to be successful. The other options are not required for the rollback action. The database does not need to be shut down or in read-only mode, as NDB can perform the rollback operation online. The patch does not need to be applied on Grid home only, as NDB can roll back patches applied on both Grid home and Database home. References:
* Nutanix Certified Professional - Database Automation (NCP-DB) v6.5, Section 4 - Operate and Maintain an NDB Environment, Objective 4.4: Determine the correct method to apply Linux OS patches
* Nutanix Database Management & Automation (NDMA) Course, Module 5: Nutanix Database Service (NDB) Patching, Lesson 5.1: Patching Overview, Topic: Patching Concepts
* [Nutanix Database Service (NDB) User Guide], Chapter 7: Patching, Section: Rolling Back a Patch