Goodwill already exist in the books is written off by:

The correct answer is Option (1) → Debiting old partners’ capital accounts in their old profit sharing ratio

Goodwill that already stands in the books was built up while the old partners shared the profits, so on admission it is written off against the old partners’ capital accounts in their old profit sharing ratio. The Goodwill A/c is credited to close it, and the capital accounts, which bear the loss, are debited.

Old Partners’ Capital A/cs (individually)     Dr.
    To Goodwill A/c
(Existing goodwill written off in the old ratio)