Explanation:

- When a partner introduces additional capital or gives a loan, the interest on the loan is calculated based on the loan amount.

- The loan amount provided is Rs 40,000.

- The correct option depends on the interest rate applied to the loan.

- Assuming an interest rate of 6%, the interest for a year would be Rs 2,400.

- Option 2: Rs 2,400 - This is correct if the interest rate is 6%.

- Option 1: Rs 4,200 - This would imply an interest rate of 10.5%.

- Option 3: Nil - This would mean no interest is paid.

- Option 4: Rs 1,800 - This would suggest an interest rate of 4.5%.