Explanation:

Undue influence:
Undue influence is a form of pressure or persuasion exerted on a person by someone in a position of power or authority. It occurs when one party takes advantage of their position to exploit or manipulate another party into making a decision that is not in their best interest.

In the given scenario, the master is in a position of power and authority over the servant. The master asks the servant to sell the goods to him at a price less than the market price. This can be seen as exerting undue influence on the servant.

Avoidance of contract:
When a contract is formed under undue influence, the party under the influence may have the right to avoid the contract. Avoidance of a contract means that the party can choose to cancel or revoke the contract, making it legally unenforceable.

In this case, the servant can avoid the contract based on undue influence. The master, being in a position of power, is taking advantage of the servant and pressuring them to sell the goods at a price that is against their best interest. This can be seen as an unfair and exploitative situation, and the servant has the right to avoid the contract.

Other options:
- Coercion: Coercion refers to the use of force or threats to make someone do something against their will. While the master is pressuring the servant, there is no indication of the use of force or threats in the given scenario.
- Fraud: Fraud involves intentional misrepresentation or deception to induce someone into entering a contract. There is no indication of fraud in the given scenario as the master is not misrepresenting any information or deceiving the servant.
- Mistake: Mistake refers to an error or misunderstanding about a material fact of the contract. There is no indication of a mistake in the given scenario as both parties are aware of the terms and conditions of the contract.

Therefore, the correct answer is option D) Undue influence. The servant can avoid the contract on the ground of undue influence exerted by the master.