A /21 subnet mask means 21 bits are network bits:
8 + 8 + 5 = 21 # leaves 11 bits for hosts.
Subnet mask in binary: 11111111.11111111.11111000.00000000
Converted to decimal: 255.255.248.0
Therefore:
A). /19 = 255.255.224.0
B). /20 = 255.255.240.0
# C. /21 = 255.255.248.0 # correct
D). /22 = 255.255.252.0
Answer correction: The correct option is C. 255.255.248.0, not B.
References (CompTIA Network+ N10-009):
Domain: Networking Concepts - Subnetting, CIDR notation, dotted decimal masks.

Ping sends ICMP Echo Request packets and waits for Echo Replies to verify host reachability and measure round-trip time.
A). tcpdump captures packets but does not test reachability.
B). netstat displays open ports and network sessions.
C). nslookup queries DNS servers for name resolution.
References (CompTIA Network+ N10-009):
Domain: Networking Concepts - ICMP operation, troubleshooting tools.

Troubleshooting poor performance of a newly installed access point involves multiple steps. Checking for network bottlenecks and ensuring the device firmware is up to date are crucial first steps. The document confirms:"Network bottlenecks can severely limit the performance of even the fastest wireless access points, so it's essential to verify that no other devices are causing a slowdown. In addition, keeping firmware updated ensures optimal performance and security."

Single Sign-On (SSO) enables a user to access multiple resources or applications with one set of credentials, improving usability and security. The document confirms:
"Single Sign-On (SSO) allows a user to authenticate once and gain access to multiple resources or applications without needing to log in again for each. It streamlines the login process and improves security by reducing the number of passwords that need to be managed."

IPv4 addresses are divided into classes:
Class A: Supports 16,777,214 hosts (large enterprises).
Class B: Supports 65,534 hosts (medium to large networks).
Class C: Supports 254 hosts (small to medium networks).
Class D: Used for multicast, not for assigning IPs to hosts.
Step-by-step Calculation:
The network will have 150 users initially, with a projected growth of 10 users, totaling 160 users.
Each user has two devices, so 160 × 2 = 320 IP addresses needed.
A Class C subnet has 254 usable IPs by default, which is not sufficient.
A Class B subnet can support thousands of hosts, making it the most appropriate option.
Incorrect Options:
A). Class D: Reserved for multicast, not for host assignments.
C). Class A: Overkill for a network of this size.
D). Class C: Cannot support 320 hosts without subnetting, making Class B the best choice.
Reference:
CompTIA Network+ N10-009 Official Study Guide - Chapter on IP Addressing and Subnetting