i) According to section 202 of the Indian Contract Act, 1872, where the agent has himself an interest in the property which forms the subject matter of the agency, the agency cannot, in the absence of an express contract, be terminated to the prejudice of such interest. \nIn other words, when the agent is personally interested in the subject matter of agency, the agency becomes irrevocable. \nIn the given question, A gives authority to B to sell A’s land, and to pay himself, out of the proceeds, the debts due to him from A. \nAs per the facts of the question and provision of law, A cannot revoke this authority, nor it can be terminated by his insanity.\nii) According to section 191 of the Indian Contract Act, 1872, a “Sub agent” is a person employed by, and acting under the control of, the original agent in the business of the agency. \nSection 210 provides that, the termination of the authority of an agent causes the termination (subject to the rules regarding the termination of an agent’s authority) of the authority of all sub-agents appointed by him. \nIn the given question, B is the agent of A, and C is the agent of B. Hence, C becomes a sub-agent. \nThus, when A revokes the authority of B (agent), it results in termination of authority of sub-agent appointed by B i.e. C (sub-agent).