Which statement about sockets is correct?

• A. A socket designates a specific program on a host identified by a port number on the host's IP address.
• B. A socket is the same as a physical network interface.
• C. A socket guarantees encrypted communication by default.
• D. A socket is identified only by an IP address without a port.

Answer: (A)

A socket is the software endpoint that lets a program send and receive data over a network by tying together a host’s IP address and a port number with a transport protocol. This combination uniquely identifies a communication path to a specific running program on a given host. The port number is what demultiplexes traffic on the host so that data arrives at the correct program, even if many programs are active on the same machine.

That’s why the best statement says a socket designates a specific program on a host identified by a port on the host’s IP address. It captures the essential idea: the IP address tells you which machine, the port tells you which program, and the transport protocol defines how the data is carried.

The other statements don’t fit because a socket is not a physical network interface; it’s a software abstraction. Encryption isn’t guaranteed by default—whether data is encrypted depends on the protocol or application (like TLS or IPsec). And a socket isn’t identified by an IP address alone; the port is essential to specify which process on the host should handle the traffic.