A redundant cluster of devices is a group of devices that can provide backup or failover functionality in case of a hardware failure or a network attack.
Layer 2 devices operate at the data link layer of the OSI model and are responsible for forwarding frames based on MAC addresses. They include switches, bridges, and NICs.
Multiple routers are not Layer 2 devices, but Layer 3 devices that operate at the network layer of the OSI model and are responsible for forwarding packets based on IP addresses. Therefore, option A is incorrect.
Multiple switches are Layer 2 devices that can provide redundancy and scalability in the network by using protocols such as spanning tree, link aggregation, and VLANs. They can also support Layer 3 functions such as routing and inter-VLAN routing. Therefore, option B is the correct answer.
Multiple firewalls are not Layer 2 devices, but Layer 4 devices that operate at the transport layer of the OSI model and are responsible for filtering traffic based on ports and protocols. They can also provide security services such as NAT, VPN, and IDS. Therefore, option C is incorrect.
Multiple budges is a typo and should be multiple bridges. Bridges are Layer 2 devices that can divide a network into segments and reduce collisions. However, they are less efficient and less intelligent than switches, and they are rarely used in modern networks. Therefore, option D is incorrect.
Reference:
CompTIA Network+ N10-008 Study Guide, Chapter 2: Network Devices, pages 47-48, 51-52, 55-56, 59-60.
Professor Messer's Network+ Video Course, Section 1.1: Network Devices, videos 1.1.1 - 1.1.4, 1.1.6, 1.1.7.
Cisco Press: Fully Redundant Layer 2 and Layer 3 Designs

An extended service set (ESS) is a wireless network that consists of multiple access points (APs) that share the same SSID and are connected by a wired network. An ESS allows wireless clients to roam seamlessly between different APs without losing connectivity. A basic service set (BSS) is a wireless network that consists of a single AP and its associated clients. An independent basic service set (IBSS) is a wireless network that consists of a group of clients that communicate directly without an AP. A unified service set is not a standard term for a wireless network. Reference: https://partners.comptia.org/docs/default-source/resources/comptia-network-n10-008-exam-objectives-(2-0), https://en.wikipedia.org/wiki/Service_set_(802.11_network)

The default credentials are the username and password that come with a device or service when it is first installed or configured. They are often easy to guess or find online, which makes them vulnerable to unauthorized access or attacks. The default credentials should be changed to something unique and strong as soon as possible to avoid this situation. If the default credentials were not changed, someone could have accessed the SOHO router and changed the WiFi settings without the employees' knowledge. Reference: https://www.comptia.org/blog/network-security-basics-6-easy-ways-to-protect-your-network

DNS poisoning is a type of attack that modifies the DNS records of a domain name to point to a malicious IP address instead of the legitimate one. This can result in users being directed to cloned websites that are stealing credentials, even if they enter the correct URL for the website. The incorrect DNS server address on the user's PC could be a sign of DNS poisoning, as the attacker could have compromised the DNS server or spoofed its response to redirect the user's queries. Reference: https://www.comptia.org/blog/what-is-dns-poisoning

A denial-of-service (DoS) attack is an example of an attack where an attacker sends more connection requests than a server can handle, causing the server to crash. A DoS attack is a type of cyberattack that aims to disrupt the normal functioning of a network service or resource by overwhelming it with excessive or malformed traffic. A DoS attack can prevent legitimate users from accessing the service or resource, resulting in degraded performance, unavailability, or data loss. A DoS attack can target various network layers, protocols, or components, such as servers, routers, firewalls, or applications. Reference: [CompTIA Network+ Certification Exam Objectives], What Is a Denial-of-Service (DoS) Attack? | Cisco