Where both the parties are under mistake as to matter of fact, the agreement is void under

Option (1) is correct: Section 20 of the Indian Contract Act, 1872 states that agreement is void, where both the parties are under mistake as to matter of fact. Option (2) is incorrect: Section 21 of the Indian Contract Act, 1872 provides effects of mistake as to law. Option (3) is incorrect: Section 22 of the Indian Contract Act, 1872 provides contract caused by mistake of one party as to matter of fact. Option (4) is incorrect: Section 23 of the Indian Contract Act, 1872 provides what consideration and objects are lawful.