Final answer:
IPv4 uses 32 bits for addressing, allowing for about 4.3 billion unique addresses, while IPv6 uses 128 bits, which accommodates a vastly larger number of unique addresses. Option a) 32, 128 is correct.
Step-by-step explanation:
The number of bits used for addressing with IPv4 (Internet Protocol version 4) and IPv6 (Internet Protocol version 6), respectively, are 32 bits and 128 bits. This means that for IPv4, the address space allows for 232 possible unique addresses, which is about 4.3 billion addresses. In contrast, IPv6 uses 128 bits for addressing, significantly increasing the address space to 2128 possible addresses, which is an almost inconceivable number and more than enough for the foreseeable future of networked devices on the internet.