The correct answer is D. Mutually agreed ratio.
The capital of all the partners must be in a mutually agreed ratio after the admission of a new partner. This is because the admission of a new partner changes the ownership structure of the partnership, and the existing partners must agree on how the new partner’s capital will be divided.
Option A is incorrect because the new profit sharing ratio is not necessarily the same as the capital ratio. The partners may agree to a different profit sharing ratio, even if the capital ratio is equal.
Option B is incorrect because the old profit sharing ratio is no longer valid after the admission of a new partner. The new profit sharing ratio must be agreed upon by all the partners.
Option C is incorrect because the capital of the partners does not have to be equal. The partners may agree on any capital ratio that they choose.