The IP header size is

15*32 Bits = 480 Bits = 60 Bytes is the maximum size of an Internet Header (IP header). This is why the header can maximum only be 60 bytes long. The smallest header size is 20 bytes, with a value of 5 in the IHL field (0101). Thus, the IP header is between 20 and 60 bytes in length.

Final Answer: Hence, the correct option is A i.e,20 to 60 bytes long.