The correct answer is A. 3,900.
The face value of each debenture is Rs. 100. The company issued the debentures at a discount of 10%. This means that the investors paid Rs. 90 for each debenture. The total amount raised by the company by issuing debentures is Rs. 3,60,000. The number of debentures issued is calculated as follows:
Total amount raised / Face value of each debenture = Number of debentures issued
3,60,000 / 90 = 3,900
Therefore, the number of debentures issued is 3,900.
Option B is incorrect because it is the face value of each debenture. Option C is incorrect because it is the total amount raised by the company by issuing debentures. Option D is incorrect because it is the number of debentures that would have been issued if the debentures were issued at par.