In which way can the IPv6 address of 2031:0000:130F:0000:0000:09C0:876A:130B be expressed
most efficiently?

A.
2031:0:130F:0:0:09C0:876A:130B

B.
2031::130F::9C0:876A:130B

C.
2031:0:130F::9C0:876A:130B

D.
2031:0:130F:0:0:9C0:876A:130B

Explanation:
IPv6 Addressing Notation
IP addresses change significantly with IPv6. IPv6 addresses are 16 bytes (128 bits) long rather
than four bytes (32 bits). This larger size means that IPv6 supports more than
300, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000 possible addresses! As an
increasing number of cell phones and other consumer electronics expand their networking
capability and require their own addresses, the smaller IPv4 address space will eventually run out
and IPv6 become mandatory.
IPv6 addresses are generally written in the following form:
hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh
In this full notation, pairs of IPv6 bytes are separated by a colon and each byte in turns is
represented as a pair of hexadecimal numbers, like in the following example:
E3D7:0000:0000:0000:51F4:9BC8:C0A8:6420
As shown above, IPv6 addresses commonly contain many bytes with a zero value. Shorthand
notation in
IPv6 removes these values from the text representation (though the bytes are still present in the
actual network address) as follows:

E3D7::51F4:9BC8:C0A8:6420
Finally, many IPv6 addresses are extensions of IPv4 addresses. In these cases, the rightmost four
bytes of an IPv6 address (the rightmost two byte pairs) may be rewritten in the IPv4 notation.
Converting the above example to mixed notation yields E3D7::51F4:9BC8:192.168.100.32
IPv6 addresses may be written in any of the full, shorthand or mixed notation illustrated above.

http://compnetworking.about.com/od/tcpiptutorials/a/ipaddrnotation.htm