After removing the virus from the server, the administrator should perform the following actions to mitigate the issue from reoccurring and to maintain high availability:
Run a vulnerability scanner on the server to identify any other potential weaknesses or exposures that could be exploited by attackers.
Patch the vulnerability that allowed the virus to infect the server in the first place, using the latest updates from the database software vendor or a trusted source.
Update the antivirus software on the server to ensure it has the most recent virus definitions and can detect and prevent future infections. The other options are either unnecessary or counterproductive for this scenario. Repartitioning the hard drive, reformatting the OS, removing the database software, or air gapping the server from the network would cause downtime and data loss, while enabling a host firewall would not prevent a virus infection from within the network. References: CompTIA Server+ Certification Exam Objectives, Domain 5.0: Security, Objective 5.2: Given a scenario involving a security threat/vulnerability/risk, implement appropriate mitigation techniques.

The storage protocol that the administrator is most likely using to save data to the location \server1\ITDept\ is CIFS. CIFS (Common Internet File System) is a protocol that allows file sharing and remote access over a network. CIFS is based on SMB (Server Message Block), which is a protocol that enables communication between devices on a network. CIFS uses UNC (Universal Naming Convention) paths to identify network resources, such as files or folders. A UNC path has the format \servername\sharename\path\filename. In this case, server1 is the name of the server, ITDept is the name of the shared folder, and \ is the path within the shared folder.

The administrator should use a subnet mask of 255.255.255.0 for this setup. A 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 network portion identifies the specific network that the IP address belongs to, while the host portion identifies the specific device within that network. The subnet mask is usually written in dotted decimal notation, where each octet represents eight bits of the binary number. A 1 in the binary number means that the corresponding bit in the IP address is part of the network portion, while a 0 means that it is part of the host portion. For example, a subnet mask of 255.255.255.0 means that the first 24 bits (three octets) of the IP address are used for the network portion and the last 8 bits (one octet) are used for the host portion. This subnet mask allows up to 254 hosts per network (2^8 - 2). In this case, the IP address of 10.20.10.15 and the default gateway of 10.20.10.254 belong to the same network of 10.20.10.0/24 (where /24 indicates the number of bits used for the network portion), which can be defined by using a subnet mask of 255.255.255.0.

A core installation is a type of installation method that is best suited to meet the company policy that states no one is to log in directly to the server. A core installation is a minimal installation option that is available when deploying some editions of Windows Server. A core installation includes most but not all server roles and features, but does not include a graphical user interface (GUI). A core installation can only be managed remotely using command-line tools such as PowerShell or Windows Admin Center, or using graphical tools such as Server Manager or Remote Desktop from another computer. This reduces the attack surface, resource consumption, and maintenance requirements of the server. A GUI installation is a type of installation method that includes a graphical user interface (GUI) and allows local or remote management using graphical tools or command-line tools. A virtualized installation is a type of installation method that involves creating and running one or more virtual machines on a physical host using a hypervisor such as Hyper-V or VMware. A clone installation is a type of installation method that involves creating an exact copy of an existing server's configuration and data on another server using tools such as Sysprep or Clonezilla. References:
https://www.howtogeek.com/67469/the-beginners-guide-to-shell-scripting-the-basics/
https://www.howtogeek.com/443611/how-to-encrypt-your-macs-system-drive-removable-devices-and-individua
https://www.howtogeek.com/199068/how-to-upgrade-your-existing-hard-drive-in-under-an-hour/

Link Aggregation: Involves combining multiple physical network interfaces into a single logical interface. This creates increased bandwidth, improved fault tolerance, and load balancing, where traffic can be distributed across all links in the group. (CompTIA Server+ Objectives SK0-004: 2.4) Why other options are incorrect:
Most recently used algorithm: A concept used in memory management, not network traffic distribution.
Active-passive configuration: Used for failover with only one interface active at a time.
Failover: Ensures service continuity if an interface fails but does not inherently distribute load across multiple links.