Explanation:

Unilateral mistake refers to a situation where only one party to the contract is mistaken about a material fact. In such a case, the contract is still considered valid. The following points explain why the correct answer is option 'C':

No mutual mistake: A unilateral mistake is different from a mutual mistake, which occurs when both parties to the contract are mistaken about a material fact. In the case of a mutual mistake, the contract is considered voidable, as both parties did not have a meeting of minds.

No misrepresentation or fraud: In the case of a unilateral mistake, there is no misrepresentation or fraud involved. The mistaken party simply made an error in judgment or fact. As such, the contract remains valid.

No unconscionable terms: If the terms of the contract are not unconscionable, then a unilateral mistake does not affect the validity of the contract. Unconscionable terms refer to clauses that are so one-sided or oppressive that they would be deemed unfair.

No undue influence or duress: A unilateral mistake is also different from undue influence or duress, which refer to situations where one party uses coercion or pressure to force the other party to enter into the contract. In such cases, the contract is voidable.

Conclusion:

In conclusion, the correct answer to the question is option 'C'. A unilateral mistake does not affect the validity of a contract as long as there is no misrepresentation, fraud, unconscionable terms, undue influence, or duress involved.