Which of the following is the default mask of the IP 178.25.3.0?

(A) 255.0.0.0
(B) 255.255.0.0
(C) 255.255.255.0
(D) 255.255.255.255

255.255.0.0 is the correct answer.

Description	Class A	Class B	Class C
First octet range	1 – 126	128 – 191	192 – 223
Valid network numbers	1.0.0.0 – 126.0.0.0	128.0.0.0 – 191.255.0.0	192.0.0.0 – 223.255.255.0
Default mask	255.0.0.0	255.255.0.0	255.255.255.0