This practice exam question broke my brain.... What do you guys think is correct?

Which of the following IPv6 addresses are valid, choose 4?

  1. ::
  2. ::192:168:0:1
  3. 2000::
  4. 2001:3452:4952:2837::
  5. 2002:c0a8:101::42
  6. 2003:dead:beef:4dad:23:46:bb:101

My original guess was that 1 and 2 were not valid addresses. But I guess it depends on what the CIDR notation is?

-Adam