Amount realised from unrecorded asset will be credited to :

Realisation A/c

The correct answer is option (1) : Realisation A/c

The unrecorded asset has been already transferred to the realisation account. So any amount realised from this asset is related with the realisation account not asset account. On receiving money on realisation, cash or bank balance is increased. So, Increase in cash is debited and realisation account is credited. The journal entry for this-
Cash A/c Dr.
  To Realisation A/c