Explanation:

- Section 20 of the Indian Contract Act deals with the concept of a bilateral mistake. A bilateral mistake is when both parties involved in a contract are mistaken about a fundamental fact related to the agreement.

- When there is a bilateral mistake, the contract is considered void as the misunderstanding affects the very essence of the agreement.

- Here are the options provided for which section addresses bilateral mistakes:

- Option 1: Section 19 pertains to voidability of agreements without free consent, like when there is fraud or misrepresentation.

- Option 2: Section 20 is indeed about bilateral mistakes, confirming that both parties are under a mistaken belief.

- Option 3: Section 21 addresses mistakes of law, focusing on misunderstandings regarding the legal aspects.

- Option 4: Section 22 highlights unilateral mistakes, where only one party is mistaken about a fact.

Your chosen answer aligns with the correct section concerning bilateral mistakes: .