Which of the following is an IP address that is private (i.

This is a valid Class B reserved address. For Class B networks, the reserved addresses are 172.16.0.0 - 172.31.255.255.

The private IP address ranges are defined within RFC 1918:

RFC 1918 private ip address range

The following answers are incorrect:

172.12.42.5 Is incorrect because it is not a Class B reserved address.

172.140.42.5 Is incorrect because it is not a Class B reserved address.

172.15.42.5 Is incorrect because it is not a Class B reserved address.