Which of the following protocol is a network layer

Solution

Why this is correct:
ICMP is a network-layer protocol used to send error messages and operational information (e.g., “host unreachable”, “time exceeded”) about problems in the delivery of IP packets. Routers and hosts use ICMP to report issues and diagnostics (ping, traceroute use ICMP). Why the others are wrong:

• 1 (HTTP): Application-layer protocol used for web communication (requests/responses), not network-layer error reporting.
• 2 (FTP): Application-layer protocol for file transfers, not for reporting network errors.
• 3 (ARP): Link-layer / protocol for mapping IP addresses to MAC addresses (not used for reporting network-layer errors).