A cable tester is a tool that can verify the integrity and functionality of a network cable. It can measure the electrical characteristics of the cable, such as resistance, capacitance, and impedance, and detect any faults or defects, such as shorts, opens, or crosstalk. A cable tester can help the network administrator troubleshoot the problem by determining if the cable is faulty or not. A tone generator is a tool that can send an audible signal through a cable to help locate and identify it. A multimeter is a tool that can measure voltage, current, and resistance of electrical circuits. An optical time-domain reflectometer (OTDR) is a tool that can test the quality and length of fiber optic cables.
References: CompTIA Network+ Certification Exam Objectives Version 7.0 (N10-007), Objective 2.3: Given a scenario, use the appropriate tool to support wired or wireless networks.

A biometric reader is a device that scans a person's physical characteristics, such as fingerprints, iris, or face, and compares them to a database of authorized users. A biometric reader can be used to restrict access to a server room and prevent unauthorized entry. A biometric reader provides a high level of security and cannot be easily bypassed or duplicated.

* Encryption is the process of transforming data into an unreadable format using a secret key or algorithm.
It can protect sensitive information from unauthorized access or theft, even if the device is lost or stolen.
* Factory reset is the process of restoring a device to its original settings and deleting all user data and applications. It can be used to erase personal information from a device before selling or disposing of it, but it does not prevent data recovery by forensic tools. Therefore, option A is incorrect.
* Autolock is the feature that automatically locks a device after a period of inactivity or when the power button is pressed. It can prevent unauthorized access to a device by requiring a passcode, pattern, fingerprint, or face recognition to unlock it. However, it does not protect the data stored on the device from being extracted by other means. Therefore, option B is incorrect.
* Two-factor authentication is the method of verifying a user's identity by requiring two pieces of evidence, such as a password and a code sent to a phone or email. It can enhance the security of online accounts and services, but it does not apply to the data stored on a device. Therefore, option D is incorrect.
References:
* CompTIA Network+ N10-008 Study Guide, Chapter 9: Network Security, pages 403-404, 407-408,
411-412.
* Professor Messer's Network+ Video Course, Section 5.1: Network Security Devices and Technologies, videos 5.1.1 - 5.1.3, 5.1.6, 5.1.7.
* CompTIA Network+ (N10-008) Sample Questions, Question 15.

Explanation
Nmap (Network Mapper) is a free and open source command line tool that can be used to scan a network for all connected hosts, detect the types of operating systems running on all devices, discover all services offered by hosts on the network, find open ports, and detect security risks. Nmap is commonly used by system administrators and security professionals to audit a network's security and identify possible vulnerabilities.
Nmap can be used to discover active hosts, scan ports, fingerprint operating systems, detect running services, and more. Reference: CompTIA Network+ Study Manual, 8th Edition, page 592.