Step 1: Understanding the rule of oral evidence under The Bharatiya Sakshya Adhiniyam, 2023.
As per the Act, when the terms of a contract have been reduced to writing, no oral evidence is allowed to contradict, vary, add to, or subtract from the written terms, except under a few specific exceptions. These exceptions mainly include cases of fraud, intimidation, illegality, failure of consideration, or the existence of a separate oral agreement that does not contradict the written document.
Step 2: Examine each option in relation to the rule.
Option (1): Here, the written contract concerns delivery of indigo. The oral evidence relates to a \textit{different and independent transaction}, i.e., payment for other indigo sold previously. Since the oral statement does not alter or contradict the written agreement, this oral evidence is admissible. Hence, this option is correct.
Option (2): This states that B agreed in writing to pay on 1st March, but there was an oral agreement that payment would be postponed till 31st March. This contradicts the written contract and is therefore not admissible. One cannot use oral evidence to directly contradict a written contractual term about the date of payment. Thus, this statement is incorrect as per the Act.
Option (3): Evidence of misrepresentation is always admissible because the Act allows oral evidence to prove fraud, misrepresentation, intimidation, or illegality even when there is a written contract. Hence, this option is correct.
Option (4): When a contract is silent about the time of payment, parties may bring in oral evidence to prove that the goods were supplied on credit for a specific term. Since no written term is being contradicted, this oral evidence is admissible. Therefore, this option is correct.
Step 3: Final Conclusion.
Only Option (2) directly contradicts the written terms of the contract and is therefore inadmissible. This makes it the incorrect statement as per The Bharatiya Sakshya Adhiniyam, 2023.