Answer: (ii) 255.0.0.0

Why: Class A uses the first 8 bits as the network id (first octet 1–126), so the default mask is $255.0.0.0$ i.e. /8, leaving 24 bits for hosts ($2^{24}-2$ hosts). Option (i) 127.0.0.1 is the loopback address, not a mask, and (iii)/(iv) 255.255.255.0 (/24) is the class C default mask.