If at the time of admission, some positive balance of Profit and Loss A/c appears in the books, it will be transferred to:

The correct option is Old Partner's Capital Account.

Reasoning:
When a new partner is admitted into a partnership firm, any accumulated profits or losses existing in the books of accounts prior to the admission belong strictly to the existing (old) partners. This is because these profits or losses were earned or incurred in the period before the new partner joined the firm.

A positive balance in the Profit and Loss Account represents accumulated profits (credit balance). At the time of admission, this accumulated profit must be distributed among the old partners in their old profit-sharing ratio.
This transfer is executed by debiting the Profit and Loss Account and crediting the Capital Accounts of the old partners.

The journal entry for this adjustment is:
Profit and Loss A/c ... Debit
    To Old Partners' Capital/Current A/cs (in old profit-sharing ratio)

Therefore, the positive balance of the Profit and Loss Account is transferred to the Old Partner's Capital Account.