The administrator should perform an antivirus scan on all servers within the cluster and reboot each server, and block access to 208.206.12.9 from all servers on the network. These actions will help to remove any malware that may have infected the application server and prevent any further unauthorized traffic to the known-bad public IP address. An antivirus scan can detect and remove malicious software that may be sending data to an external source, and a reboot can clear any temporary files or processes that may be related to the malware. Blocking access to 208.206.12.9 from all servers on the network can prevent any future attempts to communicate with the malicious IP address.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 3, Lesson 3.4, Objective 3.4; Chapter 6, Lesson 6.2, Objective 6.2

Application consistent backup is a method of backing up data that ensures the integrity and consistency of the application state. It involves notifying the application to flush its data from memory to disk and quiescing any write operations before taking a snapshot of the data. If the databases were not backed up to be application consistent, they might contain incomplete or corrupted data that cannot be restored properly.
References:
CompTIA Server+ Certification Exam Objectives1, page 12
What is Application Consistent Backup and How to Achieve It2
Application-Consistent Backups3

The most likely cause of the internet issue is B. The DHCP scope is full.
A DHCP scope is a range of IP addresses that a DHCP server can assign to DHCP clients on a network. A DHCP scope has a start address and an end address, and it can also have some excluded addresses that are not available for lease. A DHCP scope can have various options, such as subnet mask, default gateway, DNS server, etc., that are applied to the DHCP clients along with the IP address. A DHCP scope also has a lease time, which is the duration that a DHCP client can use an IP address before renewing it or releasing it. A DHCP scope can have reservations, which are fixed IP addresses that are assigned to specific DHCP clients based on their MAC addresses12 If a DHCP scope is full, it means that there are no more IP addresses available for lease in the scope. This can happen if the number of DHCP clients exceeds the number of IP addresses in the scope, or if the lease time is too long and the IP addresses are not released or reused frequently enough. If a DHCP scope is full, any new or existing DHCP clients that request an IP address from the DHCP server will not receive one, and they will not be able to access the network or the internet12 In this scenario, users are able to connect to the wireless network, but they are unable to access the internet.
The network administrator verifies connectivity to all network devices, and there are no ISP outages. The server administrator removes the old address leases from the active leases pool, which allows users to access the internet. This indicates that the DHCP scope is full, and that removing the old leases frees up some IP addresses for lease in the scope. Therefore, option B is the most likely cause of the internet issue.

To comply with the user requirements, the best options are to install the OS on a RAID 1 array, configure RAID 5 for the application data, and use SSD hard drives for the data application array. Here is why:
RAID 1 is a mirroring technique that creates an exact copy of data on two disks. This provides redundancy and fault tolerance in case of hard drive failure. RAID 1 also improves read performance since either disk can be read at the same time. Therefore, installing the OS on a RAID 1 array meets the first requirement of separating the OS from the application data and protecting it from hard drive failure.
RAID 5 is a striping technique with parity that distributes data and parity blocks across three or more disks. This provides improved performance and storage efficiency compared to RAID 1, as well as fault tolerance in case of a single disk failure. Therefore, configuring RAID 5 for the application data meets the second and third requirements of providing high IOPS performance and data availability.
SSD hard drives are solid-state drives that use flash memory to store data. They have no moving parts and offer faster read and write speeds, lower latency, and lower power consumption than traditional HDDs. Therefore, using SSD hard drives for the data application array meets the second requirement of providing high IOPS performance.
References:
https://phoenixnap.com/kb/raid-levels-and-types
https://en.wikipedia.org/wiki/Standard_RAID_levels

The subnet mask is most likely containing an error that prevents the application server from communicating with the newly installed database server. The subnet mask is a binary number that defines how many bits of an IP address are used for the network portion and how many bits are used for the host portion. The subnet mask determines which devices belong to the same network or subnet and can communicate directly with each other without routing or switching devices. The subnet mask of the database server is 255.255.O.O, which means that all 32 bits of its IP address are used for the network portion and none for the host portion, which is invalid and makes it unreachable by any other device on any network or subnet. The subnet mask of the application server is 255.O.O.O, which means that only 8 bits of its IP address are used for the network portion and 24 bits are used for the host portion, which is also uncommon and makes it incompatible with most networks or subnets. References: [CompTIA Server+ Certification Exam Objectives], Domain 4.0: Networking, Objective
4.1: Given a scenario, configure network settings for servers.