Unrecorded liability, when paid on dissolution of a firm is debited to..............

Realisation A/c

The correct answer is option 2- Realisation A/c.

For settlement of any unrecorded liability:
Realisation A/c Dr.
      To Bank A/c
(Liability is paid off)

Realisation account is debited as it is a liability which has to be paid by the firm.
Bank account is credited as settlement of liability reduces the bank balance of the firm.