Final answer:
Each group of 4 hex digits in an IPv6 address contains 16 bits, as there are 4 bits per hex digit. A full IPv6 address has eight such groups, totaling 128 bits.
Step-by-step explanation:
In an IPv6 address, each group of 4 hex digits, also known as a 'hextet,' contains 16 bits. Since one hexadecimal digit represents 4 bits, just multiply the number of hexadecimal digits by 4 to find the number of bits: 4 hex digits * 4 bits per hex digit = 16 bits per group. Therefore, a full IPv6 address, which is typically written in eight groups of four hexadecimal digits separated by colons, contains 8 * 16 = 128 bits in total.