The correct answer is A. Rs. 3,000.
In the absence of a partnership deed, the interest on capital is payable at 6% per annum. The partner introduced an additional capital of Rs. 50,000 on 1st June 2018. The interest for the period from 1st June 2018 to 31st March 2019 is therefore Rs. 50,000 x 6% x 9/12 = Rs. 3,000.
Option B is incorrect because the interest is payable at 6% per annum, not 5%.
Option C is incorrect because the interest is payable for the period from 1st June 2018 to 31st March 2019, which is 9 months.
Option D is incorrect because the interest is payable on the entire amount of capital introduced, not just on the amount of capital introduced after the partnership deed was signed.