router

[logistic_guy]

here is the question

Your router has the following IP address on Ethernet0: $\displaystyle 172.16.2.1/23$. Which of the following can be valid host IDs on the LAN interface attached to the router? (Choose two.)

A. $\displaystyle 172.16.0.5$
B. $\displaystyle 172.16.1.100$
C. $\displaystyle 172.16.1.198$
D. $\displaystyle 172.16.2.255$
E. $\displaystyle 172.16.3.0$
F. $\displaystyle 172.16.3.255$


my attemb
i know this IP $\displaystyle 172.16.2.1$ belong to class $\displaystyle B$ and the range of IP addresses in class $\displaystyle B$ is from $\displaystyle 128.0.0.0$ to $\displaystyle 191.255.255.255$
so all option given is within the range
i'm confusedwhy some IPs is valid and some is invalid