Which is the compressed format of the IPv6 address 2002:0042:0010:c400:0000:0000:0000:0909?

To compress the IPv6 address 2002:0042:0010:c400:0000:0000:0000:0909, we apply the following rules:

1. Omit leading zeros in each 16-bit block.
2. Replace one or more consecutive blocks of zeros with a double colon (::). This can be done only once in an address.

Using these rules, the compressed format of the IPv6 address is:

2002:42:10:c400::909

Explanation of the options:

1. 2002:42:10:c400::909: Correct. It correctly omits leading zeros and replaces the consecutive blocks of zeros with a double colon.
2. 200:420:110:c4b::910:0:90: Incorrect. This changes the values in the original address, altering its meaning.
3. 2002:4200::25:1090:0:99: Incorrect. This changes the values in the original address and does not accurately represent the original blocks.
4. 2002:42::25:1090:0:99: Incorrect. This also changes the values in the original address and does not accurately represent the original blocks.