A sniffer tool is a software or hardware device that can capture and analyze network traffic. In a switched Ethernet environment, where each port on a switch is connected to a single device, a sniffer tool can only see the traffic that is destined for or originated from the device it is attached to. However, an attacker can use various techniques to overcome this limitation and sniff the traffic of other devices on the same network. One of these techniques is MAC flooding, which exploits the finite memory of the switch's MAC address table.
The attacker sends a large number of frames with different source MAC addresses to the switch, which fills up the MAC address table and causes the switch to enter a fail-open mode, where it broadcasts all incoming frames to all ports, regardless of the destination MAC address. This way, the attacker can see all the traffic on the network and capture it with a sniffer tool.
The other options are less likely or less effective techniques for sniffing a switched Ethernet network.
Compromising physical security to plug into the network directly may allow the attacker to sniff the traffic of the device they are connected to, but not the traffic of other devices on the network. Using a Trojan horse with in-built sniffing capability may allow the attacker to sniff the traffic of the infected device, but not the traffic of other devices on the network, unless the Trojan horse also performs MAC flooding or other techniques to bypass the switch. Using passive sniffing, which involves listening to the network traffic without sending any packets, may provide significant stealth advantages, but it does not help the attacker to see the traffic of other devices on the network, unless the switch is already in fail-open mode or the attacker uses other techniques to induce it. References:
* Sniffing: A Beginners Guide In 4 Important Points
* How can I run a packet sniffer on a Router or Switch
* Detection of Sniffers in an Ethernet Network

The ethical hacker conducted Test 1, which is a TCP/IP stack fingerprinting technique that uses the SYN and ECN-Echo flags to determine the OS of the target system. The SYN flag is used to initiate a TCP connection, and the ECN-Echo flag is used to indicate that the sender supports Explicit Congestion Notification (ECN), which is a mechanism to reduce network congestion. Different OSes have different implementations and responses to these flags, which can reveal their identity. For example, Windows XP and 2000 will reply with SYN and ECN-Echo flags set, while Linux will reply with only SYN flag set. By sending a TCP packet with these flags enabled to an open TCP port and observing the reply, the ethical hacker can probe the nature of the response and subsequently determine the OS fingerprint.
The ethical hacker adopted this specific approach because it is an advanced and stealthy technique that can evade some firewalls and intrusion detection systems (IDS) that may block or alert other types of packets, such as NULL, FIN, or Xmas packets. Moreover, this technique can provide more accurate and reliable results than other techniques, such as banner grabbing or passive analysis, that may depend on the availability or validity of the information provided by the target system.
The other options are not correct, as they describe different tests and reasons. Test 3 is a TCP/IP stack fingerprinting technique that uses the URG, PSH, SYN, and FIN flags to determine the OS of the target system. Test 2 is a TCP/IP stack fingerprinting technique that uses a NULL packet, which is a TCP packet with no flags enabled, to determine the OS of the target system. Test 6 is a TCP/IP stack fingerprinting technique that uses the ACK flag, which is used to acknowledge the receipt of a TCP segment, to determine the OS of the target system. References:
* OS and Application Fingerprinting | SANS Institute
* Operating System Fingerprinting | SpringerLink
* OS and Application Fingerprinting - community.akamai.com
* What is OS Fingerprinting and Techniques - Zerosuniverse

One may append the comment "-" operator along with the String for the username and whole avoid executing the password segment of the SQL query. Everything when the - operator would be considered as comment and not dead.
To launch such an attack, the value passed for name could be 'OR '1'='1' ; -Statement = "SELECT * FROM
'CustomerDB' WHERE 'name' = ' "+ userName + " ' AND 'password' = ' " + passwd + " ' ; " Statement = "SELECT * FROM 'CustomerDB' WHERE 'name' = ' ' OR '1'='1';- + " ' AND 'password' = '
" + passwd + " ' ; "
All the records from the customer database would be listed.
Yet, another variation of the SQL Injection Attack can be conducted in dbms systems that allow multiple SQL injection statements. Here, we will also create use of the vulnerability in sure dbms whereby a user provided field isn't strongly used in or isn't checked for sort constraints.
This could take place once a numeric field is to be employed in a SQL statement; but, the programmer makes no checks to validate that the user supplied input is numeric.
Variation is an evasion technique whereby the attacker can easily evade any comparison statement. The attacker does this by placing characters such as "' or '1'='1'" in any basic injection statement such as "or 1=1" or with other accepted SQL comments.
Evasion Technique: Variation Variation is an evasion technique whereby the attacker can easily evade any comparison statement. The attacker does this by placing characters such as "' or '1'='1'" in any basic injection statement such as "or 1=1" or with other accepted SQL comments. The SQL interprets this as a comparison between two strings or characters instead of two numeric values. As the evaluation of two strings yields a true statement, similarly, the evaluation of two numeric values yields a true statement, thus rendering the evaluation of the complete query unaffected. It is also possible to write many other signatures; thus, there are infinite possibilities of variation as well. The main aim of the attacker is to have a WHERE statement that is always evaluated as "true" so that any mathematical or string comparison can be used, where the SQL can perform the same.

https://en.wikipedia.org/wiki/RADIUS
Remote Authentication Dial-In User Service (RADIUS) is a networking protocol that provides centralized authentication, authorization, and accounting (AAA) management for users who connect and use a network service.
RADIUS is a client/server protocol that runs in the application layer, and can use either TCP or UDP. Network access servers, which control access to a network, usually contain a RADIUS client component that communicates with the RADIUS server. RADIUS is often the back-end of choice for 802.1X authentication.
A RADIUS server is usually a background process running on UNIX or Microsoft Windows.
Authentication and authorization
The user or machine sends a request to a Network Access Server (NAS) to gain access to a particular network resource using access credentials. The credentials are passed to the NAS device via the link-layer protocol-for example, Point-to-Point Protocol (PPP) in the case of many dialup or DSL providers or posted in an HTTPS secure web form.
In turn, the NAS sends a RADIUS Access Request message to the RADIUS server, requesting authorization to grant access via the RADIUS protocol.
This request includes access credentials, typically in the form of username and password or security certificate provided by the user. Additionally, the request may contain other information which the NAS knows about the user, such as its network address or phone number, and information regarding the user's physical point of attachment to the NAS.
The RADIUS server checks that the information is correct using authentication schemes such as PAP, CHAP or EAP. The user's proof of identification is verified, along with, optionally, other information related to the request, such as the user's network address or phone number, account status, and specific network service access privileges. Historically, RADIUS servers checked the user's information against a locally stored flat-file database. Modern RADIUS servers can do this or can refer to external sources-commonly SQL, Kerberos, LDAP, or Active Directory servers-to verify the user's credentials.
Shape Description automatically generated with medium confidence

The RADIUS server then returns one of three responses to the NAS:
1) Access-Reject,
2) Access-Challenge,
3) Access-Accept.
Access-Reject
The user is unconditionally denied access to all requested network resources. Reasons may include failure to provide proof of identification or an unknown or inactive user account.
Access-Challenge
Requests additional information from the user such as a secondary password, PIN, token, or card.
Access-Challenge is also used in more complex authentication dialogs where a secure tunnel is established between the user machine and the Radius Server in a way that the access credentials are hidden from the NAS.
Access-Accept
The user is granted access. Once the user is authenticated, the RADIUS server will often check that the user is authorized to use the network service requested. A given user may be allowed to use a company's wireless network, but not its VPN service, for example. Again, this information may be stored locally on the RADIUS server or may be looked up in an external source such as LDAP or Active Directory.