The requirement is to support over 300 hosts. The subnet mask 255.255.254.0 (or /23) provides 512 addresses, 510 of which are usable - ideal for around 300 devices.
* 255.255.0.0 (/16) provides too many addresses.
* 255.255.192.0 (/18) gives 16384 addresses - overkill.
* 255.255.255.254 is invalid for host assignments (only 2 addresses, 0 usable).
From Andrew Ramdayal's guide:
"To support 300 hosts, a /23 subnet (255.255.254.0) offers 510 usable addresses - the most efficient choice without excessive overhead."