If a ping to 10.0.100.19 is unreachable, the most likely issue is that users are on the wrong subnet and cannot communicate with the server.

Breakdown of Options:

A. The users are on the wrong subnet. ✅ Correct answer. If users are on a different subnet without proper routing, they won't reach the server.

B. The DHCP server renewed the lease. – Would change the client’s IP, but the server’s static IP should remain unchanged.

C. The IP address was not reserved. – DHCP reservations matter for dynamic IPs, but RDP servers typically have static IPs.

D. The hostname was changed. – Would affect DNS resolution, but pinging the IP directly would still work.